Skeletal implant

ABSTRACT

Skeletal implant of the type to be used for connecting at least two elements of the skeleton. The implant has at least two parts. Each of the parts is capable of being connected to one of the elements. The implant also uses at least one shock-absorbing device located between the at least two parts. The shock-absorbing device has an adjustable coefficient of resistance.

RELATED APPLICATION

[0001] The present application is a continuation of U.S. applicationSer. No. 09/200,855, filed Nov. 30, 1998, the disclosure of which isexpressly incorporated by reference herein in its entirety. U.S.application Ser. No. 09/200,855 is a continuation-in-part of U.S.application Ser. No. 08/897,673, filed on Jul. 21, 1997, now abandoned,the priority of which is claimed under 35 USC 120 and the disclosure ofwhich is incorporated by reference thereto in its entirety.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a skeletal implant, and moreparticularly to an implant of this type to be used for connecting atleast two elements of the skeleton, which implant is embodied in atleast two parts, each of which is capable of being connected to one ofthese elements.

[0004] According to a first aspect of the invention, it relates to aconsolidating and/or connecting implant, and more particularly to animplant of this type to be used to consolidate a connection between twobone elements, of the type comprising a first part designed to beattached to one of the elements and a second part designed to beattached to the other element.

[0005] 2. Background and Material Information

[0006] There are known implants of this type that are capable of beingused, for example, in the case of a performance of a bone graft orduring the formation of a callus following a fracture. The two ends ofthe implant, which are rigidly connected to one another, for examplebecause they are embodied in one piece, are each attached, for examplescrewed, to a bone element located on either side of the graft. When thegraft has consolidated, the implant can be removed.

[0007] However, there are numerous cases where the implant is left inplace. This is particularly the case when the implant is used to replacea bone structure which is impossible to restore or to construct.

[0008] In such cases, the rigidity of the implant, which is oftenindispensable at the beginning of the implantation, during the formationof the callus, later constitutes a drawback. In effect, the bonestructures no longer sustain sufficient mechanical stress. Therefore,they do not reconstitute themselves in an optimal way, thisreconstitution being tied to a satisfactory stressing of the bone, thedisturbance of which has consequences which can result in post-surgicalpain that is very difficult to treat.

[0009] Moreover, when the implant is to be used to connect two boneelements which are normally capable of moving relative to one another,as in the case of a rachidian implant, this rigidity results in afunctional handicap in the patient in whom it is implanted, andexcessive stress on the neighboring joints.

SUMMARY OF THE INVENTION

[0010] The object of the invention is, among other things, to eliminatethese drawbacks.

[0011] According to a second aspect of the invention, it relates to anarticulated implant, and more particularly to an implant of this typeintended either to be intercalated between two bone elements in relativemotion, such as an artificial intervertebral disk, or to replace a jointor an element of a joint, such as an artificial head of the femur.

[0012] As regards the intercalated implant, it can be beneficial toassist the adjacent bone structures and the ligaments during rapid, oreven violent movements. On the other hand, it may be preferable to allowthese structures and ligaments to work during slow movements or simplestatic load in order to prevent atrophy or weakening.

[0013] As regards the articulated implant itself, a completely rigidstructure fully transmits the shocks and vibrations to the other elementof the joint, resulting in a risk of dystrophy or rupture of this otherelement.

[0014] Also, once a surgical skeleton implant is implanted nomodification can be made to adapt the implant to the changing needs ofthe patients.

[0015] Another object of the present invention is to eliminate thesedrawbacks.

[0016] To this end, the subject of the invention is a skeletal implantof the type to be used for connecting at least two elements of theskeleton, which implant is embodied in at least two parts, each of whichis capable of being connected to one of these elements, these partsbeing movable with respect to each other, characterized in that itcomprises between these two parts at least one adjustable deviceresponsive to non invasive control means, said control means beingpreferably located on said implant, to exert an adjustable force, forexample a distraction or compression force, between said parts, and/orto authorise an adjustable displacement between said parts between astarting position and a displaced position in which said parts should,at least temporarily, be maintained, and/or to secure a damping effectwith an adjustable coefficient of resistance.

[0017] It is noted, first of all, that the adjustment can be discrete aswell as continuous, and for example, can include only two positions ofadjustment.

[0018] It is known that a shock-absorbing device is a device generallycomprising two chambers of variable volume filled with a hydraulic fluidand connected by a calibrated opening. A device of this type is intendedto <<cushion>> the movements between two elements, one of which isconnected to a structure of one of the chambers, the other beingconnected to an element in which the calibrated opening is formed.

[0019] When the two elements move relative to one another, the volumesof the two chambers vary in inverse proportion to one another, thehydraulic fluid being laminated at the level of the calibrated opening.The result is a force which opposes the relative movement between thetwo elements which, as will be shown, is proportional to the speed ofthis movement.

[0020] Used within the scope of the invention, a device of this typeapplied to an implant of the consolidating and/or connecting type hasthe advantage of allowing the bone structures to function, and thus todevelop, in a practically normal way at moderate relative speeds betweenthe bone elements connected by the implant, particularly in case ofstatic stresses. On the other hand, the greater the relative speeds,particularly in the case of voluntary rapid movement or shock, that is,dynamic stresses, the greater the portion of the stress absorbed by theimplant.

[0021] The result is that the osteo-ligamentous structure, weakened bythe situation which justified the insertion of the implant, cannevertheless function and thus reconstitute normally as long as thestresses remain moderate. But the greater these stresses, the more thenatural structure is assisted by the implant.

[0022] Moreover, the coefficient of resistance being adjustable, it ispossible to reduce it progressively as the bone structure reconstitutes.The latter can also sustain more and more dynamic stresses until,eventually, it returns to normal functioning.

[0023] It is noted that it has already been suggested in the prior artto endow prostheses with viscous and/or elastic means intended to absorbshocks. Likewise, it is well known to provide, in certain prostheses,regulating or adjusting means. However, no prosthesis with a functionalcharacteristic of viscous resistance has yet been proposed wherein thecoefficient of resistance would be adjustable. This combination isessential in the primary function of the invention, which is to allow aprogressive reconstitution of the bone structure and an optimalcontinuous adaptation to the state of this structure.

[0024] When applied to an articulated implant, the invention also makesit possible to give the articulation greater flexibility, which, as inthe prior art, allows it to absorb shocks, but in this case also allowsthe neighboring bone structures and ligaments to work.

[0025] Finally, the consequence of this shock-absorbing characteristicis to protect the implant itself, as well as joints located above andbelow the implant, from shocks.

[0026] In one particular embodiment, the implant comprises removablemeans for locking the shock-absorbing device at a predetermined length.

[0027] The implant according to the invention, in this embodiment, canfunction during a first period in the traditional way, like a rigidimplant. This phase of functioning is for example that of the formationof the callus in the case of a graft. During a second period, thelocking means are removed and the implant functions according to theinvention, exerting between the elements to which it is connected aforce which is proportional to their relative speed and is therefore afunction of the stresses exerted in the graft.

[0028] In another particular embodiment, the implant comprises means forlimiting the travel of the shock-absorbing device.

[0029] This has the advantage of rendering the implant rigid in the casewhere the stresses reach a certain limit. Thus, there is no risk ofreaching the rupture stress point.

[0030] Advantageously, these means for limiting the travel areadjustable.

[0031] The travel of the shock-absorbing device can therefore be adaptedto the patient and possibly increased progressively as the graftstrengthens.

[0032] An implant according to the invention can be embodied in the formof an elongated element such as a screw, or a pin such as a coxofemoralprosthesis pin, or even the neck, the body or the head of a femoralprosthesis, comprising two end parts connected by a flexible middlepart, the middle part comprising two chambers filled with hydraulicfluid, disposed on either side of a neutral axis and designed such thatone of them increases volume while the other decreases in volume whenthe implant flexes, these chambers being linked by at least onecalibrated conduit.

[0033] This embodiment can be used to connect the two parts of afractured bone to one another, for example the femur at the level of theneck or the diaphysis. The screw is positioned so that its middle partis located at the point of the fracture, with its neutral axis disposedas near as possible to the plane of maximum flexion under stress. Thus,after the formation of the callus, the implant will continue to assistit during sudden efforts, the hydraulic fluid being forced from thechamber whose volume decreases to the chamber whose volume increases,through the calibrated opening. On the other hand, the callus willsustain the static stresses on its own.

[0034] More particularly, these end parts can be connected by an elasticwall delimiting these chambers with a peripheral bellows.

[0035] As will be seen below, it is often advantageous to add elasticcomponent to the viscous component of the implant's behavior.

[0036] The calibrated conduit can be embodied in the form of borings inat least one of the end parts.

[0037] This produces a very compact embodiment that is well suited tothe embodiment of the implant in the form of a screw.

[0038] Advantageously, a valve is provided on the calibrated conduit.

[0039] This valve can initially be closed during the formation of thecallus. Thus the implant is perfectly rigid and behaves like a classicscrew. The valve is then opened so that the implant functions accordingto the invention, with its shock-absorbing function. A valve with aprogressive opening makes also makes it possible to provide the functionfor adjusting the coefficient of resistance.

[0040] The control of the valve is preferably housed at the end of theimplant, nearest the skin.

[0041] Thus, a completely non-invasive intervention allows the valve tobe opened and possibly adjusted.

[0042] In a particular embodiment which is especially well suited to theperformance of a bone graft for the purpose of replacing an injuredvertebra, the shock-absorbing device comprises at least one chamberformed of two semi-chambers joined by a bellows, each of thesemi-chambers being connected to one of the parts of the implant, thischamber being filled with a hydraulic fluid, and at least one calibratedopening provided in a wall of this chamber for connecting this chamberwith another chamber.

[0043] This disposition has the advantage of being very compact andpreventing the relative slippage of the mechanical parts, with theresulting risk of hydraulic fluid leakage. However, in certain cases atraditional cylinder-and-piston shock-absorber may be preferred.

[0044] More particularly, these semi-chambers can be in the form ofcouples whose openings face on another.

[0045] The above-mentioned locking means can in this case comprise aremovable elongated locking element, inserted into a fold of the bellowsso as to prevent it from collapsing.

[0046] The elongated locking element can be embodied in any appropriateway, for example in the form of a metal beaded chain.

[0047] The above-mentioned means for limiting the travel can comprise astop ring screwed onto one of the semi-chambers and designed tocooperate with a shoulder of the other semi-chamber to prevent the twosemi-chambers from moving toward one another beyond a certain limit.

[0048] The other chamber can be housed in a supporting skirt mounted onone of the semi-chambers around the calibrated opening, opposite theother semi chamber.

[0049] This other chamber can also be formed of two semi-chambers joinedby a bellows.

[0050] In a preferred embodiment, the implant according to the inventionalso includes elastic means between these two parts.

[0051] In effect, it is often beneficial for the resistance to therelative displacement of the two parts of the implant to be proportionalnot only to the speed of this displacement, but also to the value ofthis displacement itself relative to a nominal position. Thus, theimplant's assistance to the surrounding bone structure is even moreefficient when they are farther apart than their normal configuration.

[0052] Advantageously, the coefficient of elasticity is adjustable.

[0053] Thus, it is possible to adjust the elasticity of the implant and,for example, to render it increasingly flexible as the surroundingstructures re-establish themselves.

[0054] This type of elasticity can be obtained in an implant comprisingtwo chambers filled with hydraulic fluid and joined by a calibratedopening, at least one of which chambers contains a compression ampullaat ambient pressure with elastic walls.

[0055] When a movement between the two parts of the implant begins, itproduces a pressure variation in the chambers, and thus an elasticreaction of the compressible ampulla.

[0056] The wall of this ampulla can have progressive elasticity, one ofthe chambers being capable of being joined to a source of fluid underpressure.

[0057] Thus, in this case, it is possible to regulate the elasticity ofthe implant by adjusting the pressure chambers.

[0058] Means can be provided for adjusting the cross section of thecalibrated opening.

[0059] In particular, these means for adjusting the cross section of thecalibrated opening can comprise a hydraulically controlled needle valve.

[0060] Another subject of the present invention is an implant of thetype described above wherein the shock-absorbing device at least twochambers, specifically tow low-pressure chambers whose walls are made ofelastic material, these chambers joined by at least one calibratedconduit and filled with hydraulic fluid, and designed to sustain adifferential pressure variation during a relative movement of theelements.

[0061] This type of design makes it possible to easily obtain implantwhich, as above, not only have a viscous region which is a function ofthe speed, but also an elastic resistance which is a function of thedisplacement.

[0062] In this case, the cross-section of the conduit can advantageouslybe determined by prevailing pressure in a high-pressure chamber which iscapable of comprising this conduit.

[0063] As a result of this design, the coefficient of resistance of theimplant can be regulated very easily by adjusting pressure in thehigh-pressure chamber.

[0064] In particular, one of the low-pressure chambers can have a wallof relatively low rigidity relative to the rigidity of the walls of theother chamber.

[0065] This design allows the implant to function even when the twochambers are not stressed differently. During a movement which createsexcessive pressure, the pressure increases more in the rigid-walledchamber, resulting in a flow of the hydraulic fluid from this chamber tothe chamber with the less rigid wall, and thus a shock-absorbing effect.

[0066] In one particular embodiment, a high-pressure chamber and alow-pressure chamber can be connected, in the low-pressure tohigh-pressure direction, by a non-return valve.

[0067] As will be seen, this disposition makes it possible to increasethe pressure difference between the high-pressure and low-pressurechambers. It also makes it possible to maintain this difference despitepossible leaks in to high-pressure to low-pressure direction.

[0068] The anti-return valve can comprise a flexible tube connected tothe low-pressure chamber, one free end of which is inserted into a freeend of a tube connected to the high-pressure chamber.

[0069] This type of valve is very small and also has the advantage ofbeing even tightly closed when the pressure difference is greater.

[0070] Preferably, it is also arranged for these chambers to beconnected by a pressure regulation valve in parallel with theanti-return valve.

[0071] It will be seen that the anti-return valve is preferably disposedbetween the high-rigidity, low-pressure chamber and the high-pressurechamber.

[0072] In one particular embodiment, the implant according to theinvention comprises a first annular low-pressure chamber, and a secondrotating chamber in the center of the first chamber, the calibratedconduits being formed radially in the wall separating the two chambers.

[0073] Advantageously, the outer wall of the first low-press chamber isrelatively thin and the wall separating the two low-pressure chambers isrelatively thick.

[0074] This implant can comprise at least one annular high-pressurechamber formed within the thickness of the wall separating the twolow-pressure chambers, and designed to compress the calibrated counts.

[0075] In another embodiment, this conduit is at lease partiallyembodied in the form of a tube of elastic material surrounded by a tubeis substantially more rigid, these tubes being joined into rings attheir ends, the compressed volume between the two tubes forming ahigh-pressure chamber.

[0076] In another particular embodiment, the implant is substantiallydisk-shaped, comprising a plurality of low-pressure chambers in sectors,joined by the calibrated conduits, which alternate inside the thicknessof the disk with the high-pressure chambers.

[0077] Advantageously, the implant according to the invention comprisesme for adjusting the distance between the element it connects.

[0078] This type of design makes it possible, in particular, toalleviate possible post-operative pain by adjusting this distanceappropriately. It is also particularly advantageous in the case ofprostheses intended for children who are still growing.

[0079] These adjusting means can comprise a bellows designed to receivea hydraulic fluid, and means for connecting this bellows to a source offluid under pressure.

[0080] Another subject of the invention is a pair of implants asdescribed above, the low-pressure chamber of each of the implants beingconnected by the anti-return valve to the high-pressure chamber of theother implant.

[0081] A pair of implants of this type can particularly be provided, inthe case of a graft of the vertebral column, to assist the graft in caseof lateral flexion.

[0082] More generally, a pair of implants according to the invention caninclude means for automatically adapting to the movements of the wearerof the implants.

[0083] Up to this point, bone consolidation implants embodied accordingto the invention have been described. It will now be shown that theinvention is also well suited to the embodiment of articulated implants.

[0084] In this case, each part of an implant as described above isarticulated to the other.

[0085] More particularly, these parts can have complementary surfaceswhich rest against one another, forming a ball-and-socket joint.

[0086] An articulated implant of this type can include, in particular, apivot integral with one of the parts and housed in a space formedbetween a plurality of low-pressure chambers in the form of sections,which are integral with the other part of the implant and joined by thecalibrated conduits, which themselves alternate with high-pressurechambers.

[0087] These embodiments are suitable as intervertebral disks.

[0088] In a particular application to a coxofemoral joint, the implantaccording to the invention comprises an articulating hollow sphere whosewall is open so as to allow the insertion of the end of a connectingpin, the shock-absorbing device being disposed inside this spherebetween the wall of the latter and the end of the connecting pin.

[0089] More particularly, this shock-absorbing device can comprise anend element of the connecting pin designed to slide through a slot of apartition inside the sphere, which partition delimits two chambers inthe sphere, and at least one calibrated opening is formed inside thisend element between two chambers.

[0090] In another embodiment, this shock-absorbing device can include anend element of the connecting pin disposed between two shock-absorbingelements, each of which includes at least two low-pressure chamberswhose walls are made of elastic material, these chambers being connectedby at least one calibrated conduit and filled with hydraulic fluid, anddesigned to sustain a differential pressure variation during a relativemovement of the sphere and the connecting pin.

[0091] Another subject of the invention is a pair of implants asdescribed above, used particularly within the scope of an arthrodesis ofthe vertebral column, each of the implants being mechanically connectedin series to a connecting pin of a known type.

[0092] More particularly, each of the implants can include means foradjusting the distance between the two element it connects.

[0093] It is thus possible, using a pair of implants of this type notonly to perform the arthrodesis, but also to adjust the angle and thedistance between the two parts of the vertebral column connected by theprosthesis.

[0094] In one particular mode of embodiment, these adjusting meansinclude, for each implant, an expandable element such as a bellows,designed to receive a hydraulic fluid, and means for connecting thisbellows to a source of fluid under pressure.

[0095] This source of fluid under pressure can comprise a high-pressurefluid reservoir.

[0096] Advantageously, this high-pressure reservoir is common to bothimplants, each expandable element is also connected to a low-pressurereservoir, and an expandable refill cell is mechanically connected inseries to each pin, each refill cell being connected to thehigh-pressure and low-pressure reservoirs by two anti-return valves, oneof which allows a flow of fluid from the low-pressure reservoir to therefill cell, the other allowing a flow of fluid from the refill cell tothe high-pressure reservoir.

[0097] It will be seen that this type of design makes it possible toproduce a pump activated by the movements of the wearer of the implants.

[0098] In another particular embodiment, the above-mentioned pair ofimplants is formed of implants in which the shock-absorbing devicecomprises at least two chambers, these chambers being connected by atleast one calibrated conduit and filled with hydraulic fluid anddesigned to sustain a differential pressure variation during a relativemovement of these elements, the cross-section of this calibrated conduitbe determined by the prevailing pressure in a high-pressure chamber, andthe high-pressure chambers of the implants are connected to thehigh-pressure reservoir by a controllable valve.

[0099] Another subject of the invention is a skeletal implant asdescribed above, specifically belonging to a pair of implants,

[0100] which includes sensors of physical quantities, including pressuresupplied with electric power and controlled from outside the body in anon-invasive way, and designed to transmit their information to displaymeans.

[0101] More particularly, this implant also include adjusting actuatorswhich arm also supplied with electric power and controlled from outsidethe body in a non-invasive way.

[0102] In facts the implants which were described have a variable lengthor dimension, the two parts or ends of the implant being able to moveapart from one another or approach one another actively and/orpassively, for example along the longitudinal axis of the implant, byvirtue of the interposition of a deformable element, for example ahydraulic element, control means and/or regulating means being providedso as to make it possible to obtain a change in dimension of the implantin order to modify the distance between the two bone elements and/or toensure an adjustable viscous or viscoelastic damping emitting a slowmovement between the two bone elements and also counteracting a moreabrupt displacement.

[0103] If necessary, a sufficiently high hydraulic pressure can bemaintained by using the effect of a mechanical pump, actuated by themovements of the body, with a pressure-limiting valve flap, cooperatingwith a low-pressure reservoir.

[0104] For example, double implants consisting of two individualimplants can be disposed respectively on either side of the spine inorder to connect two vertebrae, each of the two elements thus beingfixed to a lower vertebra via an anchoring means, such as a pediclescrew, and to an upper vertebra, either adjacent or more distant,likewise each time by an anchor means, such as a pedicle screw.

[0105] In the case of a double implant consisting of two individualimplants acting on the same skeletal structures, the two individualimplants hydraulically can be interconnected in such a way as to permitpivoting movements of the bone elements relative to one another, namelya lateral pivoting in the frontal plane of the spine, by increasing thelength of one of the individual implants and concomitantly reducing thelength of the other implant, for a correction of deformation and/or adamping of lateral flexion.

[0106] By virtue of control means, for example noninvasive means of themagnetic type, it is possible to effect the desired modifications to thedimension of the individual implants and/or the modifications to thedamping coefficient of the element acting as a damper. Moreover, meanscan be provided for automatically modifying the damping coefficient orthe viscosity as a function of the movements of the body.

[0107] In brief, the present invention proposes realizing and perfectingan implantable device comprising at least one implant equipped with twoend parts which can be fixed, by anchoring means, on at least twoelements or parts of the skeleton, and comprising means of displacement,preferably at least partially reversible, between the said two ends,these means being arranged to provoke and/or maintain a displacementbetween the said elements of the skeleton

[0108] This displacement can be a rectilinear and/or curveddisplacement, for example it can be a displacement of elongation, alsocalled distraction, or a displacement of shortening, called compressionor a displacement in rotation, it being possible for this rotation to beisolated or, on the contrary, to be combined with a distraction or acompression.

[0109] In the simplest embodiment, in which the said displacement meansare capable of maintaining but not provoking the displacement, thesedisplacement means are controlled by control means, preferably noninvasive ones, which make it possible to release them so as to allow thepatient, or another party, to modify the relative position of the twoportions or elements of the skeleton, after which the said control meansare actuated in order to block the implant in this new position, aninverse or reversible displacement still remaining possible if one actsonce more on the control means, for example in the case where thedisplacements would have been too great.

[0110] In another preferred embodiment of the invention, the saiddisplacement means include a motor means with which it is possible toimpose a displacement between the said ends by exerting a force betweenthem.

[0111] In a particular embodiment, this force can be exertedtemporarily, that is to say for quite a brief instant, for the purposeof provoking a therapeutically desirable displacement between the twoportions or elements of the skeleton, such a displacement often beingintended for a small amplitude, since it is rapidly impeded by theanatomical structures which must not be traumatized. At the end of thisinstant, the control means make it possible to block the two endsrelative to one another and to maintain the implant in its new position.

[0112] In another embodiment, by contrast, the said displacement meansare capable of exerting an anatomically active permanent force betweenthe said two ends, it being possible for this force to be constant orvariable in such a way as to exert on the anatomical environment astress which will gradually permit an anatomically desired displacementbetween the said two portions or elements of the skeleton, these motormeans being controllable by control means with which it is possible topermit or interrupt their functioning and/or to adjust the intensity ofthe force.

[0113] If appropriate, the implant can also include viscous orviscoelastic damping means which can be used when the implant is blockedin its dimension or when the implant is freed or when it exerts itspermanent active force. Such means have been described in the abovementioned European and American applications.

[0114] The said means of displacement and, if necessary, the said motormeans can be of the hydraulic and/or mechanical and/or electrical type,a hydraulic type being preferred.

[0115] In one embodiment using hydraulic means, the implant preferablyincludes:

[0116] two parts or end elements, for example rods, each receiving atleast one means for anchoring in a skeletal part;

[0117] at least one deformable element, preferably hydraulic, interposedbetween the said two elements, and permitting a variation in dimensionand/or the creation of an active force between them;

[0118] preferably at least one high-pressure reservoir, called areserve, with which it is possible to address the high pressure, ondemand, to a functional user circuit; preferably at least onelow-pressure collection reservoir connected to the high-pressurereservoir via a pressure control valve;

[0119] preferably at least one circuit for recharging the high-pressurereservoir, comprising at least one deformable element, preferablysensitive to physical positions or movements of the body receiving theimplant, to generate a high pressure which, if so required, feeds thehigh-pressure reservoir;

[0120] at least one functional circuit, rely:

[0121] a circuit for modifying the dimension, for example the length, ofthe implant, comprising the said deformable element with which it ispossible to modify a dimension between the two end elements and/or toestablish, between the two end elements, an active force capable ofprovoking a progressive modification of the dimension between the saidend elements, the said deformable element being connected on the onehand to the high-pressure reserve reservoir by way of a first valve and,on the other hand, to the low-pressure collection reservoir by way of asecond valve in order to make it possible, as a function of the controlof the said valves, to increase and/or reduce the dimension of the saiddeformable element in order to permit or provoke a lasting modificationto the said dimension of the said individual implant, and/or

[0122] a viscous or viscoelastic damping circuit comprising:

[0123] if appropriate, an elastic element surgically interposed betweenthe said two end elements of the implant, and a hydraulic dampingelement comprising at least one deformable element sensitive to thespeed of a dimensional variation of the implant and communicating with adischarge reservoir by way of a throttle means, and control means whichcan preferably be actuated from outside the body of the patient, inorder to modify the dimension of the implant and/or the force exerted bythe implant and/or the damping properties.

[0124] Of course, one and the same piece, for example a deformableelement, can form a constituent part of several of the constituentsdefined hereinabove.

[0125] The circuit for recharging the high-pressure reservoir is in factintended to act as a very high-pressure pump, making it possible toestablish and to maintain a high pressure in a high-pressure reservoir.

[0126] Preferably, especially in the preferred case where the deformableelement of the high-pressure recharging circuit is sensitive to physicalpositions or movements of the patient receiving the implant, thisdeformable element has a small surface compared with the active .surfaceof the element which transmits to it the force originating from thebody, in such a way as to ensure a pressure-multiplying differentialeffect, it being understood that upon each stress only a small quantityof very high-pressure fluid is sent towards the high-pressure chamber.

[0127] The deformable element of the circuit for recharging thehigh-pressure reservoir can also be actuated by external means whileremaining implanted. Thus, for example, this deformable element can bein the form of a pump, preferably formed by a metal bellows, implantedon a part of the body at a point where an external pressure can beapplied to it, for example implanted on the posterior face of thesacrum, allow this pump or bellows to be actuated by hand via theexternal anatomical planes.

[0128] Alternatively, this pump could be of the magnetic orelectromagnetic type, having, for example, a movable core actuating asmall piston or bellows under the influence of an electromagnetic forceof external origin.

[0129] It will also be appreciated that the present applicationincorporates the alternatives and equivalents using non-hydraulic motorand/or damping means, ensuring the same functions of lasting andadjustable modification of dimension and/or force and/or adjustablemodification or variation of the damping coefficient.

[0130] Solely by way of example, an implant of the uniquely mechanicaltype can comprise a first end, movable in translation relative to thesecond end, and secured to a rod which is immobilized by a catch whichis sensitive to an external magnetic control means for blocking orreleasing the said rod, a motor means being interposed between the saidrod and the said second end, it being possible for this motor means tobe in the form of a spring or another precharged elastic element tendingto displace one of the ends relative to the other when the catch isreleased, it being possible for the movement to be reversible, at leastonce, for example by inserting, between the spring and the said secondend, a spring support piece which can be displaced, by virtue of othermagnetic control means, in such a way as to at least partially relax thespring. Alternatively, the implant can include several springs arrangedin parallel and capable of being used separately by release means whichare sensitive to control means.

[0131] In another embodiment, an implant can include displacement meansof the electromagnetic type, for example a solenoid with a plunger core,the solenoid being secured to one of the ends of an implant and theplunger core being secured to the other end, blocking means preferablybeing provided for immobilizing the core relative to the solenoid in atleast two different positions, the solenoid being capable of beingpowered, via a control means, from an electrical energy source, forexample an implanted battery and/or an accumulator which can berecharged by antenna transmission with transcutaneous coupling.

[0132] Such embodiments are reversible within the meaning of theinvention because, if so desired, they permit a modification in theopposite direction, at least partly, of the dimensional modificationwhich has been established.

[0133] The present invention also makes it possible to perfect themovements or forces of rotation permitted or imposed by an implant or aset of at least two individual implants in the frontal and/or sagittaland/or horizontal plane.

[0134] For example, the invention can provide implants of this type withwhich it is possible to impose symmetrical movements of rotation, thatis to say in the same direction and of the same value of rotation, ofthe pedicle screws or similar anchoring means of the two individualimplant elements, or, by contrast, antisymmetrical movements, that is tosay in opposite directions, or else independent of one another.

[0135] Generally speaking, the movement or force of rotation controlledbetween the two anchoring means of an implant according to the inventionand, where appropriate, the coordination of the movements or forces ofrotation of the anchoring means of several implants, for example theindividual implants of a double implant, will make it possible,depending on requirements, to approximate much more closely thetheoretically possible or desirable natural movement between the twobone parts to which the anchoring means are fixed, so as to imposeprogressive displacements for example for corrections, and/orprogressively modifiable damping, ranging, for example, from rigidityduring a phase of bone consolidation or healing to progressive mobility,making it possible, for example, to safeguard a joint.

[0136] The skeletal implant has a first and a second end element, meansfor anchoring in bone parts, which means are connected respectively tothe said first and second end elements, at least one deformable elementconnected respectively to the said first and second anchoring means, andmeans permitting a nonrectilinear movement, particularly a rotation,between the said anchoring means.

[0137] The implant can include mean permitting a rotation between thesaid end elements.

[0138] The said deformable element can be deformable in rotation.

[0139] The implant can include means permitting a rotation of at leastone of the said anchoring means relative to the end piece to which it isconnected.

[0140] The abovementioned movement of rotation can also be combined withmovements of translation, in such a way that the resulting movement canbe a complex nonrectilinear displacement.

[0141] According to one refinement, the skeletal implant, having a firstand a second end element, means for anchoring in bone parts, for exampleby way of screws, such as, for example, pedicle screws situated at thesaid ends, at least one deformable element, for example a hydraulicelement, containing an incompressible hydraulic fluid and interposedbetween the two end elements, and means for actuating the deformableelement, for example, if necessary, hydraulic circuit means connected tothe said at least one deformable element interposed between the saidends, and capable of permitting a lasting modification, preferablyobtained progressively, of the distance or the force between the saidtwo ends and/or a viscoelastic damping of the movements between the saidtwo ends, the said actuating means, for example the said hydrauliccircuit means, being sensitive to control means which can preferably beactuated from outside the body of the patient, is characterized in thatthe said fixing or anchoring means are fixed to the said two ends byarticulated attachment means, and in that the said fixing or anchoringmeans are additionally connected to one another via a rigid joiningelement which is relatively parallel to the geometric axis connectingthe said two ends of the implant and is situated at a certain distancefrom the said axis, by attachment means which are likewise articulated,for example in such a way as to form between the said four attachmentpoints a deformable quadrilateral, permitting an angular movement ofrotation of the said fixing or anchoring means relative to one another.

[0142] These articulated attachment means can consist of actualmechanical articulations or of suitably deformable joining means.

[0143] For example, the articulations can be articulations using a ballwhich is received rotatably in a seat of the end piece, this ball havinga passage through which it can receive and hold a part of an anchoringmeans, such as a pedicle screw. Of course, all other articulationprinciples such as a pivot articulation can be used.

[0144] In one embodiment, the said jointing element is situated betweenthe axis of the implant and the bone elements to which the implant isfixed, but in another embodiment the said joining element is arranged onthe other side of the axis of the implant in relation to the boneelements which are joined by the implant.

[0145] The said joining elements can be simple rigid links such as rodsor bars of invariable length

[0146] However, in another embodiment, these joining elements themselvescan include, between their ends, at least one deformable zone, whichthen makes it possible to effect displacements, such as, for example, anelongation of the implant without relative rotation of the fixing means,by simultaneous modification of the length of the actual element and ofthe joining element, and/or to effect a viscoelastic damping between thebone elements without any movement of rotation of the said fixing means.

[0147] A complex implant in accordance with the invention can be formedby using two individual implants arranged, for example, side by side,for example on either side of the spinous processes of the vertebralcolumn, with a hydraulic interconnection making it possible to effect atleast one of the following functions: antisymmetrical rotation movementof the means of one individual implant relative to the movement of theanchoring means of the other implant, symmetrical movements of the saidanchoring means, independent movements.

[0148] Of course, for the sake of simplicity, the two individualelements of a complex implant can use common hydraulic elements, suchas, for example, high-pressure reservoir, low-pressure collector, meansfor creating the high pressure, and means for controlling the hydrauliccircuit.

[0149] In another embodiment, intended to permit a rotation in atransverse plane, or, if appropriate, an oblique plane, relative to thegeneral direction of the implant, that is to say the directionconnecting the two anchoring means or screws, the skeletal implant,having a first and a second end element, means for fixing or anchoringin bone parts, for example by way of screws, for example pedicle screwssituated at the ends, at least one deformable element interposed betweenthe two end elements, and its actuating means, to permit a lastingmodification, preferably obtained progressively, of the distance betweenone end and an element removable relative to the said one end, andcontrol means, which can preferably be actuated from outside the body ofthe patient, is characterized in that the said movable element isarranged to provoke or permit a rotation of the other of the two endsabout an axis substantially parallel to the said implant.

[0150] The means by which the displacement of the said movable elementby the movement of the deformable element transforms this movement intoa movement of rotation of the said other end, and of the fixing oranchoring means which it supports, can be a means combining a screw anda nut in such a way that the movement of translation of the one provokesa movement of rotation of the other.

[0151] In a particular embodiment, the deformable element is interposedbetween the two end pieces, one of which is capable of turning, in sucha way that the deformation of the deformable element entrains at one andthe same time a rotation and a translation of one of the end elements,and thus of the anchoring means which it bears, relative to the otherend piece, translating into a helical movement of one of the end piecesrelative to the other.

[0152] In another embodiment, the two end pieces can be secured to oneanother in such a way as to remain spaced apart by an invariabledistance, the movable element then being interposed between thisassembly of end elements and the means for transform the deformation ofthe movable element into a rotation of one of the end elements relativeto the other.

[0153] In another embodiment, it is the deformable element itself whichis constructed to deform in rotation, for example by using a deformablechamber with rotary piston, according to the well-known principles ofhydraulic rotation.

[0154] Devices capable of rotation, such as have just been described,can be particularly useful in cases of severe scoliosis or seriousdegenerative destabilization of the spine. In these cases, it will forexample be possible to fix two devices according to the invention oneither side of the posterior process of the vertebra, between twovertebral levels, and to provoke rotation between the two anchoringpoints of one of the two devices, or a rotation combined with alongitudinal displacement, the other device then being capable of acomplementary movement of geometric adaptation of the displacementsimposed by the first one.

[0155] All kinds of complex nonrectilinear displacements can be obtainedby means of the intervention, for example by subjecting the displacementof an anchoring means, or of an end piece, to a cam or slide or othercurved guide.

[0156] The implant consisting of a device according to the inventionwill preferably have an external shape suitably adapted to the physicalenvironment in which it is located. For example, in particular forvertebral implants, it will be advantageous to give each of the two endsa streamlined shape so as not to disturb the adjacent tissues,especially since, by virtue of the implants according to the invention,it is possible to achieve a functional improvement which should involvethe muscles and ligaments, in contrast to arthrodesis which cause theiratrophy.

[0157] This streamlined shape can comprise an envelope, which ispreferably deformable and is applied around the implant, and of whichthe two ends which have the fixing means for the anchoring means emergefrom the envelope, the latter containing the various other components ofthe implant. The free internal volume in this envelope can preferablyserve as a low-pressure liquid reservoir. The implant preferablyincludes, inside this envelope, the movable element which can be amechanical motor or preferably a hydraulic motor, for example ahydraulic bellows, the interior of which is connected via a low-pressurevalve to the low-pressure volume formed in the envelope.

[0158] Preferably, the interior of the envelope also includes ahigh-pressure reservoir, preferably a bellows, and, again preferably, adifferential deformable element for sending liquid at very high pressureinto the high-pressure reservoir, the high-pressure reservoir beingcorrected to the movable element likewise via a high-pressure valve, thehigh-pressure value and the low-pressure valve preferably beingrelatively spaced apart from one another in order to easily permit aselective control by external control means, such as, for example,magnets.

[0159] However, in another embodiment, particularly when a succession ofindividual implants is provided at various levels of the spine, it isalso possible to provide a single high-pressure reservoir and/or asingle recharging means for recharging the high-pressure reservoirs,which is situated away from the various individual implants and isconnected to these by inextensible conduits.

[0160] The high-pressure reservoir can advantageously be designed tomaintain the liquid which it contains at high pressure, even whensignificant quantities of this liquid are sent to the motor means of theimplant, provoking a substantial reduction in the volume of liquid. Thiscan be affected, for example, by designing the high-pressure reservoirin the form of an elastically deformable reservoir of great stiffness,for example a metal bellows of great stiffness, which is expanded whenit contains the liquid at high pressure, this bellows tending to retractin order to maintain the high pressure during a substantial part of itsretraction travel. Alternatively, or in combination with such a bellows,it is also possible, in order to maintain the high value of pressure inthe reservoir, to provide an energy accumulator in the form of a cellwith an elastically deformable wall which is compressed, thus reduced involume, when the high-pressure liquid is introduced into thehigh-pressure reservoir, and which relaxes elastically while at the sametime maintaining a high pressure when liquid is withdrawn from thehigh-pressure reservoir. This energy accumulator is preferably in theform of a deformable capsule which can, for example, comprise in itsinterior an easily deformable substance or a gas, but which particularlypreferably has a substantial vacuum so as to eliminate any risk ofescape of gas.

BRIEF DESCRIPTION OF DRAWINGS

[0161] Particular embodiments of the invention will now be described, byway of a non-limiting example, in reference to the appended schematicdrawings, in which:

[0162]FIGS. 1a and 1 b schematically illustrate the principal of theinvention applied to the formation of a callus after the fracture of along bone;

[0163]FIG. 2 schematically illustrates a femoral reconstruction processafter a fracture of the neck;

[0164]FIG. 3 shows a screw according to the invention which can be usedto implement the process of FIG. 2;

[0165]FIG. 4 is a larger-scale view of the detail IV of FIG. 3;

[0166]FIG. 5 is an even larger-scale axial section of the detail IV;

[0167]FIG. 6 is a schematic axial section illustrating the functioningof this screw;

[0168]FIG. 7 is a schematic axial section of a shock-absorbing devicewhich can be used in an implant according to the invention;

[0169]FIG. 8 is a partial view of the device of FIG. 7 showing a certainnumber of improvements;

[0170]FIG. 9 is a partial section along the line IX-IX of FIG. 8;

[0171]FIG. 10 is a view in perspective of elements of FIGS. 8 and 9;

[0172]FIGS. 11a and 11 b are also partial views of the device of FIG. 7showing other improvements, in two successive phases of the utilizationof the device;

[0173]FIG. 12 is a front view in partial section of a rachidian implantembodied according to the invention;

[0174]FIG. 13 shows the utilization of two implants according to theinvention within the scope of a rachidian arthrodesis;

[0175]FIG. 14 shows in detail, in axial section, the implants of FIG.13, in section along the line XIV-XIV of FIG. 15, and theirinterconnections;

[0176]FIG. 15 is a cross-sectional view along the line XV-XV of FIG. 14;

[0177]FIG. 16 is a diagram of the device of FIGS. 13 through 15;

[0178]FIGS. 17a through 17 d illustrate the functioning of the deviceFIGS. 13 through 16;

[0179]FIG. 18 shows a top view, in partial cross-section, of anotherembodiment of a rachidian prosthesis according to the invention;

[0180]FIG. 19 is a sectional view along the line XIX-XIX of FIG. 18;

[0181]FIG. 20 is a sectional view along the line XX-XX of FIG. 19;

[0182]FIG. 21 is a sectional view along the line XXI-XXI of FIG. 18;

[0183]FIG. 22 illustrates the interconnection of the chambers of theprosthesis of FIG. 18;

[0184]FIG. 23 shows another possible assembly of two implants like thoseshown in FIG. 14;

[0185]FIG. 24 illustrates a variant of FIG. 23;

[0186]FIG. 25 is a schematic axial section of an application of theinvention to a intervertebral prosthesis;

[0187]FIG. 26 shows tho implantation of the prostheses of FIG. 25;

[0188]FIG. 27 is an axial sectional view of a “ligament” of FIG. 26;

[0189]FIG. 28 shows a schematic top view of an embodiment of anintervertebral prosthesis according to the invention;

[0190]FIG. 29 is a sectional view along the line XXIX-XXIX of FIG. 28;

[0191]FIG. 30 is a sectional view along the line XXX-XXX of FIG. 28;

[0192]FIG. 31 is a sectional view along the line XXXI-XXXI of FIG. 28;

[0193]FIG. 32 is a view in perspective showing in greater detail theimplantation of the intervertebral prosthesis of FIGS. 28 through 31;

[0194]FIG. 33 is a view in perspective of an anti-return valve which canbe used in an implant according to the invention;

[0195]FIG. 34 is an axial sectional view;

[0196]FIGS. 35 and 36 are views in perspective of a coxofemoralprosthesis embodied according to the invention;

[0197]FIG. 37 is a schematic cross-sectional view;

[0198]FIG. 38 is a sectional view of the head of the prosthesis of FIGS.35 through 37;

[0199]FIG. 39 is a partially exploded view of the prosthesis of FIGS. 35through 38;

[0200]FIG. 40 shows another implant which can be used in place of thosein FIG. 13;

[0201]FIG. 41 is a view in perspective of an element of implant of FIG.40;

[0202]FIG. 42 is an axial sectional view;

[0203]FIG. 43 is a view similar to FIG. 41 of another embodiment;

[0204]FIG. 44 is au axial sectional view of this embodiment;

[0205]FIG. 45 illustrates the functioning of the elements of FIGS. 41through 44;

[0206]FIG. 46 illustrates another mode of functioning of thisembodiment;

[0207]FIG. 47 is a schematic view of the entire hydraulic circuit of anarthrodesis of the vertebral column using implants of the same type asthe one in FIG. 40;

[0208]FIG. 49 is an electrical wiring diagram of the control of animplant according to the invention;

[0209]FIG. 51 shows a diagrammatic view of a pair of implants forantisymmetrical rotations according to a first embodiment of theinvention,

[0210]FIG. 52 shows another embodiment of such a pair of implants,

[0211]FIG. 53 shows another embodiment of such a pair of implants,

[0212]FIG. 54 shows one particular embodiment of an implant from FIG.53,

[0213]FIG. 55 shows a view of a pair of implants according to theinvention for symmetrical rotation movements according to a firstembodiment,

[0214]FIG. 56 shows a second embodiment of such a pair of implants,

[0215]FIG. 57 shows a third embodiment of a pair of implants forsymmetrical rotations,

[0216]FIG. 58 shows a view of an embodiment of an implant from FIG. 57,

[0217]FIG. 59 shows a diagrammatic view of a pair of implants, one ofwhich permits a simultaneous axial and rotational movement in a planetransverse to the general direction of the implant,

[0218]FIG. 60 shows a diagrammatic view of a pair of implants, one ofwhich permits a rotation without translation movement, in a planeperpendicular to the general direction of the implant,

[0219]FIG. 61 shows a side view of an embodiment of an implant accordingto FIG. 59,

[0220]FIG. 62 shows a front view with partial sectioning of thisimplant,

[0221]FIG. 63 shows a front view, with partial sectioning, of an implantaccording to an embodiment from FIG. 60,

[0222]FIG. 64 shows a cross section of a detailed embodiment of theinvention.

[0223] In FIGS. 51 to 60 which follow, it is assumed that the spineextends in a vertical direction and that the two individual implants arearranged on either side of the succession of spinous processes, and thatthe lower pedicle screws are screwed into a first vertebra and the upperpedicle screws are screwed into another vertebra, which may or may notbe adjacent and is arranged above the first one. The two individualelements are shown in a frontal plane which is the plane of the drawing.The result of this is that the pedicle screws should be oriented in amore or less sagittal plane, in other words more or less perpendicularto the plane of the drawing, or at any rate inclined, but for reasons ofsimplicity of representation they have been shown in the same frontalplane. Likewise, the joining elements have been shown in the samefrontal plane, whereas they should be in the perpendicular or inclinedplane which contains the pedicle screws.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0224]FIGS. 1a and 1 b represent a long bone 1 in whose middle part 2 agraft 3 has been formed, between two end elements 4 and 5.

[0225] An implant generally designated by the reference number 6, isprovided in order to consolidate the graft 3. For this purpose, theimplant 6 comprises two parts 7 and 8, each of which is screwed into oneof the bone elements 4 and 5, respectively. According to the invention,the opposite ends of the parts 7 and 8 are connected by ashock-absorbing device.

[0226] The shock absorber 9 is composed in a known way of a cylinder 10which forms two closed chambers 11 and 12 for respectively, separated bya piston head 13, mounted such that it slides in the cylinder. For thispurpose, the cylinder 10 is filled with a hydraulic fluid, which can belaminated at the level of a calibrated opened (not represented) formedin the piston head 13.

[0227] Means of any known type, also not represented, are provided foradjusting the coefficient of resistance, for example means for adjustingthe cross-section of the calibrated opening. Adjusting means of thistype are present in all embodiments described below, even in the caseswhere they are not mentioned.

[0228] The end of the part 7 of the implant is connected to a piston rod14 attached to the head 13 and passing through one of the end plates ofthe cylinder. The end of the part of the implant is connected to thecylinder 10.

[0229] Moreover, a removable rigid connecting piece 15 initiallyconnects the end pat 7 and 8 of the implant, thus making the shockabsorber 9 inactive.

[0230] The implants 6 is put in place with its connecting piece 15 (FIG.1a), which is as long as no callus has formed at the level of the graft.Due to this connecting piece, the implant behaves like a standardimplant, sustaining both the static and dynamic stresses. When thecallus has formed (FIG. 1b), the connecting piece 15 is removed orinhibited.

[0231] Since the shock absorber exerts between the parts 7 and 8 of theimplant 9 a force proportional to the relative speed of these two parts,the partially reconstituted bone will sustain all of the staticstresses. On the other hand, it will be increasingly assisted by theshock absorber as the dynamic stresses it sustains become moresubstantial, thus causing high rates of strain, in this case tensilestrain or compressive strains.

[0232]FIGS. 2 through 6 show an application of the principle explainedin reference to FIGS. 1 an and lb.

[0233] These figures show the top part of a femur 100 which hassustained a fracture at the level of the neck 101. In a known way, ascrew 103 is inserted into the body of the femur and into its head 104,in order to hold the latter in place until the formation of a callus andthe suture of the two parts separated by the fracture.

[0234] The screw 103 is embodied in two rigid substantially cylindricalparts, namely a body 105, the part of the screw nearest the skin, and athreaded point 106, the part farthest from the skin, respectively. Thepart nearest the skin comprises, at its external end, a head 107 forturning the screw 103. The two end parts are connected by a flexiblemiddle part 108.

[0235] The middle part 108 is formed by an annular bellows 109 whichconnects the peripheries of the inner ends of the body 105 and the point106. A flat elastic blade 110 also connects these two ends, which bladecontains their axis, thus allowing a relative pivoting movement betweenthe two parts 105 and 106 in a plane perpendicular to the blade, whilepreventing such a movement in the plane of the blade. The blade 110 thusforms a neutral axis in a rotation between the part 105 and 106 aroundan axis perpendicular to the axis of these parts and contained in theplane of the blade 110.

[0236] Thus, the bellows 109 and the blade 110 delimit two chambers 111and 112 disposed on either side of the neutral axis. During a bending ofthe screw, which causes a relative rotation of its parts 105 and 106around the above-mentioned axis, the volume of one of the chambers (111in FIG. 6) increases while the volume of the other (112) decreases.

[0237] The chambers 111 and 112, as well as their connecting conduits asdescribed above, are filled with a hydraulic fluid.

[0238] Borings 113 parallel to the axis of the screw each connect to oneof the chambers 111 and 112 and connect to one another through atransverse boring 114. A valve 115 (not represented it FIG. 6) mountedin the boring 114 makes it possible to open or close the connectionbetween the chambers 111 and 112, as well as to regulate thecross-section of the passage between these chambers.

[0239] The control rod 116 of the valve 115 is coaxial with the body 105of the screw, and its control head, which for example is itself a screw,is included in the head 107 of the screw. Thus it is disposed near theoutside of the body of the patient when the screw is inserted.

[0240] The screw 103 is positioned in a known way, but such that itsmiddle part 108 is disposed at the level of the fracture. Moreover, thescrew is immobilized in axial rotation in such way that the plane of theblade 110 is perpendicular to the plane of FIG. 2, in a way that canproduce a relative rotation of the parts 105 and 105 of the screw aroundan axis perpendicular to this plane and passing through the level of thepart 108.

[0241] During the implantation, the valve 115 is closed. Thus, noconnection is permitted between the chambers 111 and 112, so that thescrew is perfectly rigid throughout the time it takes for the callus toform. Once the callus has formed, a minor intervention allows access tothe control head of the valve 115, making it possible to open thisvalve, and to adjust its opening and consequently the coefficient ofresistance of the implant.

[0242]FIGS. 1a and 1 b illustrate the utilization of a standardshock-absorbing device. Generally, however, the shock-absorbing devicesused will be better adapted to the particular use to be made of them.

[0243] Thus, FIG. 7 shows a shock-absorbing device in which each of thetwo chambers 220 and 221 has a variable volume due to the presence of abellows 222 and 223, respectively.

[0244] The chamber 220 is formed of two semi-chambers in the shape ofcupels 224 and 225 whose openings face one another. These cupels areconnected by the bellows 222.

[0245] Likewise, the chamber 221 is formed of two semi-chambers, one ofwhich is constituted by a cylinder 226 welded to the outside of thebottom 227 of the cupel 225, the other of which is a cupel 228 whoseopening faces the cylinder 226. The cylinder 226 and the cupel 228 areconnected by the bellows 223.

[0246] Each of the bellows in this case is embodied in the form of atoric sector made of shoot metal welded along each of its edges and theedges of the cupels 224 and 225, in the case of the bellows 222, andalong the free edge of the cylinder 226 and the edge of the cupel 228 inthe case of the bellow 223.

[0247] The chambers 220 and 221 are filled with a hydraulic fluid andconnect through a calibrated opening 229 cut into the bottom 229 of thecupel 225 and opening into the cylinder 226. Thus, when a compressivestress is exerted on the cupels 224 and 225 of the chamber 220, tendingto push them toward one another, the volume of this chamber decreaseswhile fluid passes through the opening 229 and is force into the chamber221, whose volume increases. This force which opposes the approach ofthe cupels 224 and 225 is proportional to the approach speed, assumingthat the bellows do not exert any force, particularly of an elasticnature.

[0248] When the compression stress stops, the bellows return thechambers 220 and 221 to their original configuration.

[0249] In the embodiment represented, the chamber 221 is housed incylindrical stress. transmitting support skirt 230, welded to the bottom227 of the cupel 225 around the cylinder 226. In this case, the stressesare transmitted to the shock-absorbing device by the cupel 224 and theskirt 230, which two elements connect the parts of the implant.

[0250] In FIGS. 8 through 10, the cupel 224 comprises, in a cylindricalarea an external threading 240 onto which is screwed a stop ring 241equipped with a cooperating internal threading. One end of the ring 241faces a shoulder 242 of the cupel 225, in this case the edge of thiscupel onto which one edge of the bellows 222 is welded.

[0251] Moreover, a beaded chain 243 is engaged in the annular space 244delimited by the fold of the bellows 222, which includes the edge of the224, and the bottom of the ring 241. The beads of the chain in this casehave a diameter substantially equal to the distance at equilibriumbetween the edges of the cupels 224 and 225 which face one another. Oneend 245 of this chain exits the annular space 224 through a slot 246formed in the lateral wall of the stop ring 241, opposite the shoulder242.

[0252] During the insertion of the implant, and in the subsequentconsolidation phase, the chain 243 prevents the collapse of the bellows222 in such a way that, under compression, the device behavessubstantially like a traditional rigid implant. If the chain has adiameter smaller than the thickness of the space 244, the device has apartial shock-absorbing function in this phase.

[0253] After consolidation, the chain 243 is removed by pulling on itsend 245, the device then functioning entirely according to theshock-absorbing principal of the invention. However, a compression limitis obtained by the abutment of the edge of the ring 241 against theshoulder 242 of the cupel 225. Thus, the device once again functions,under compression, like a rigid implant.

[0254]FIGS. 11a and 11 b illustrate an alternate embodiment of thelocking system of the chain 243 of FIGS. 8 through 10. In is case anelastic needle 250 has one of its ends 251 welded to the inside of thecupel 224 of the chamber 220. Initially, the other end 252 of the needle250 is engaged in the calibrated opening 229, which it obstructs. Due tothe incompressibility of the hydraulic fluid contained in the chambersof the device, the device is perfectly rigid.

[0255] When desiring to make the device function according to theinvention, it suffices to distance the cupels 224 and 225 from oneanother enough to disengage the end 252 of the needle 250 from theopening 229. This opening is then free to allow the passage of thehydraulic fluid and cannot in any case be re-blocked by the needle 250.

[0256] The rachidian implant 260 of FIG. 12 comprises two end parts 261and 262 equipped with anchoring cones 263 and 264, respectively. Thepart 261 also includes a sleeve 265 connected to the anchoring cone by alength adjusting screw 266.

[0257] A shock-absorbing device 267, in this case the same type as thosedescribed in reference to FIGS. 7 through 11, has a cupel 224 integralwith the sleeve 265 and a skirt 230 integral with the end part 262.

[0258] An implant of this type can be used during operations forrestoring the functioning or the integrity of the vertebral column. Thevertebrae at least partially retain their structural functions in caseof static stresses. On the other hand, the implant is more active whenthe dynamic stresses are substantial.

[0259]FIG. 13 shows an arthrodesis of the vertebral column in which twopins 301 and 302 are anchored in two vertebrae 303 and 304 so that, in aknown way, they provide a connection between these two vertebrae. Thepins 301 and 302 in this case are each embodied in two parts 301′, 301″and 302′, 302″, respectively, each of these parts being connected at oneof its ends to one of the vertebrae 303 and 304, and at its other end tothe other part, by means of a device 305 according to the invention.

[0260] An example of this type of device is describe in reference toFIGS. 14 and 15, respectively in cross-section and in axial section.

[0261] The implant 305 comprise a shell constituted by two half-shells306 and 306′ which are upper and lower shells, respectively. Disposedinside this shell is an alveolar structure 307, particularly made ofsilicone, which ensures both the elastic and shock-absorbing functionsbetween the two half-shells 306 and 306′.

[0262] The structure 307 comprises an outer toric chamber 308 and asubstantially cylindrical central chamber 309, these two chambers beingseparated by a partition 310. The partition 310 is constituted in thefollowing way.

[0263] It forms a thick wall 311 of low elasticity (of high elasticrigidity) relative to the external wall 312 of the outer chamber 308.Radial conduits 313 disposed inside this wall 311 connect the chambers308 and 309. Annular chambers 314 which communicate freely with oneanother used formed between the conduits 313, which conduits 313 andchambers 314 are distributed in layers perpendicular to the axis of theprosthesis.

[0264] The lower half-shell 306 in this case is connected by a bellows315 to a base 316. Means, not represented, make it possible to injecthydraulic fluid under pressure into the chamber 317 delimited by thebottom of the half-shell 306, the bellows 315 and the base 316. It isthus possible to adjust the axial thickness of the implant 305.

[0265] Obviously, a differential adjustment of the two bellows 315 makesit possible to realign vertebrae of FIG. 13.

[0266] By providing a range of adjustment that is sufficient to allow asubstantial variation of the length of the device, it is possible toproduce an adjustable internal fixation, allow the repair of thevertebrae without the need for osseous fusion of the joints of thesevertebrae.

[0267] Other means which are not represented, but which are included formost fluid injection sites or adjusting buttons implanted under the skinof the patient, make it possible to adjust the pressure in the chambers308 and 309 on the one hand, and 314 on the other hand, the pressure atequilibrium in effect being equal in the low-pressure chambers 308 and309, and lower than the pressure in the high-pressure chamber 314.

[0268]FIG. 14 also shows that the central low-pressure chamber 309 ofeach prosthesis 305 is connected to the high-pressure chamber of theother prosthesis by conduits 318 equipped as described below.

[0269] Mounted in each conduit 318 is an anti-return valve 319 which canopen from a low-pressure chamber 309 into the correspondinghigh-pressure chamber 314, when the pressure in the chamber 309 becomeshigher than that in the chamber 314. Moreover, a pressure control valve320 is mounted in parallel with the valve 319, which valve is calibratedin a known way to establish a predetermined differential pressurebetween the low-pressure chamber 309 and the high-pressure chamber 314.

[0270] It is noted that the conduits the low-pressure chambers could, ina variant, be disposed outside the shell. One such embodiment wouldinvolve producing a conduit of this type at least partially in the formof a catheter made of elastic material surrounded by a substantiallymore rigid tube, the catheter and the tube being joined into rings attheir ends, for example by means of adhesive bonding or welding. Thehigh-pressure chamber in this case is constituted by the volume betweenthe catheter and the tube.

[0271] Refer now to FIG. 16, in which stop the same reference numbersused in FIGS. 14 and 15 have been repeated, combined with the letters Dand G for the right and left implants, respectively (seen from the rearof the patient wearing the prosthesis).

[0272] In FIG. 16, the various chambers are comparable to pressurecylinders wherein the body constitutes the chamber itself. Thesecylinder bodies are to be fixed, which means that the lower parts 301′and 302′ of the pins 301 and 302, the bases 316, and the lowerhalf-shells 306 are assumed to be fixed.

[0273] The pistons 309D′ and 309G′ and 314D′ and 314G′ illustrate thestresses exerted an the corresponding chambers by the upper half-shells306′ when the patient bends laterally, to the left in FIG. 16 as seenfrom behind. As for the pressure cylinders 308D and 308G, the elasticityof the walls is only symbolized, by the springs 321D and 321G, thepressure variations in the chambers 308 in practice resulting only inmovements of fluid though the conduits 313 due to this elasticity.

[0274] Finally, those conduits 313 are symbolized by flexiblerestrictions compressed to a greater or lesser degree by the fluidcontained in the high-pressure chambers 314.

[0275] This behavior of the left implant, which it compressed during themovement, will now be examined. Due to the thickness s of the wall 311and thus its low elasticity, the central low-pressure chamber 309 canincrease in diameter only slightly to compensate for the decrease in itsheight. The fluid it contains will then be expelled through the conduits313 to the peripheral low-pressure chamber 308. Thus, the desiredshock-absorbing function is obtained.

[0276] Furthermore, the elasticity of the wall 312, symbolized by thespring 321 of FIG. 16, will simultaneously have the tendency to resistthe expansion of the chamber 308, and therefore the entry of the fluidinto this chamber. Thus, the function of elastic resistance is obtained.

[0277] It is noted that, as the left half-shells 306 ad 306′ move closertogether, the left high-pressure chambers 314 also move loser to oneanother, which has the effect of increasing the coefficient ofresistance by reducing cross-sections of the conduit 313.

[0278] On the right side, where conversely, the half-shells 306 and 306′have a tendency to move apart, the fluid will move in the oppositedirection. Due to these rigidity of its walls, the cross-section of thechamber 309 will not vary much. But as its height, and therefore itsvolume, in increases, fluid will enter it from the chamber 308 throughthe conduits 313. The cross-sections of the latter will increase, whichwill have the effect of reducing the coefficient of resistance on thisside, thus compensating for its increase on the other side.

[0279] This elastic behavior will result from most of the stressesexerted on the lateral wall of the chamber 309.

[0280] Consequently, it is noted that during the patient's movement, theimplant essentially sustains the high-amplitude or high-speed stresses.But it is the bone graft which will sustain the moderate static loads orloads from resulting relatively slow movements. The result is areduction in the risk of osteoporosis.

[0281] It will now be seen, in reference to FIGS. 17a through 17 d, howthe differential pressure between the high-pressure and low-pressurechambers, which is essential for retaining the shock-absorbingcharacteristics of the implant, is regulate. The figures illustrate thepressure levels in the central low-pressure chamber and the highpressure chambers as a function of time.

[0282] It is assumed, in reference to FIGS. 17a through 17 d, that thepatient successively bends to his right rapidly (FIG. 17a), or slowly(FIG. 17b), straightness himself (FIG. 17c), and bends again, but to hisleft (FIG. 17d). The solid lines (HPD and BPD) relate to the rightimplant, and the broken lines (HPG and BPG) relate to the left implant.

[0283] During a rapid movement, a substantial pressure peak is observedwhich is positive on the bent side, and negative on the other side, inboth the high-pressure and low-pressure chambers. The reason why thisoccurs in the high-pressure chambers will be explained below. In thelow-pressure, it is due to the rigidity of the walls of the chambers 309and to the shock-absorbing effect of the conduits 313, which slow theflow of fluid from the chambers 309 to the chambers 308.

[0284] The time t₁ that it makes for the patient to bend to the right,during which the pressure levels vary, then stabilize, can be see inFIGS. 17a and 17 b. The respective pressure levels were substantiallyequal before the movement, by reason of symmetry, but after the movementthe pressure levels are obviously higher on the right than on the left.

[0285] When the movement is rapid enough, there is a period t₂ includedin t₁ during which the pressure in the low-pressure chamber 309 becomeshigh-pressure than the pressure in the left high-pressure chamber 314.The anti-return valve 319G then opens and allows the passage of fluidfrom the right low-pressure chambers to the left high-pressure chamber.Simultaneously, the pressure control valve 320G allows a flow and theopposite direction so as to prevent the differential pressure betweenthe high and low pressure from exceeding the set-point value.

[0286] Thus, if need be for any reason, the differential pressurepredetermined by the calibration value of the pressure control valve isre-established. This can occur continuously in the case of leaks fromthe high-pressure chambers to the low-pressure chambers, or when thelow-pressure chambers are refilled by injection, or even when anadjustment is made to increase the differential pressure between thehigh and low pressure. The device the functions like a pump controlledby the movements of the patient.

[0287] If, on the other hand, the bending movement is slow, as shown inFIG. 17b, the fluid has the time to flow from the right low-pressurechambers 309 to 308 without causing excessively high pressure levels.The anti-return valve 319G does not open.

[0288] When the patient straightens, the pressure levels change as shownin FIG. 17c. Given that the pressure levels on the right side areinitially higher than those on the left side, it is not very probablethat during the period t₃ of the movement, the prevailing low pressurein the left chamber 309 will become greater than the prevailing highpressure in the right chamber 314.

[0289] It is only when the patent bends quickly enough to the left, asrepresent in FIG. 17d, which is symmetrical to the case in FIG. 17a,that the differential pressure between the right high-pressure chamberand the left low-pressure chamber re-establishes its set-point value.The period t₄ of the movement, and the period t₂ during which the leftlow pressure becomes greater than the right high pressure, are shown inthis figure.

[0290] It is understood that what has just been described step-by-stepin reference to FIGS. 17a through 17 d actually occurs continuously whenthe patient is moving normally, successively adopting various naturalpostures. Consequently, it is noted that this results in a continualbiomechanical adaption of the implants to the stresses imposed on it bythe patient.

[0291] In light of the auto-refill principle explained in reference toFIGS. 17a through 17 d, it may be seen that the pressure points that aretoo acute will flatten out due to the fact that the fluid is laminatedas it flows into the anti-return valve. This produces an additionalshock-absorbing effect when the cell is stressed suddenly enough thatthe low pressure surpasses the high pressure. Taking into account thevariability of the coefficient of resistance as a function of the loads,as described above, this proves to be a device endowed with anadvantageous capacity for self-adjustment.

[0292] Another advantage of this mode of functioning resides in the factthat a practically continuous circulation of fluid occurs in thehydraulic circuit of the implant of the invention. This circulationavoids the risk of collapse and thus limits the need for maintenanceoperations.

[0293] Another embodiment 322 of the implants 305 is seen in FIGS. 18through 22.

[0294] The implant 322 is again embodied in the form of an alveolarstructure made of elastomer contained in a shell composed of a lowerhalf-shell 323 and an upper half shell 324.

[0295] The alveolar structure of this embodiment is in the shape of adisk and forms three low-pressure chambers 325 in the form of sectors,distributed substantially equally around the axis of the disk, at 120°from one another. The three chambers 325 connect through a network ofcalibrated conduits 326, here disposed in two transverse layers.

[0296] Three groups of high-pressure chambers 327, which communicatewith one another by any appropriate means, are disposed between thelow-pressure chambers 325. The chambers 327 are flat in shape, and eachgroup has three of them, interposed between the layers of conduits 326.The pressure in the high-pressure chambers determines the cross-sectionof the conduits 326 and thus their characteristics of viscosity.

[0297]FIG. 22 shows that the low-pressure chambers are connected to thehigh-pressure chambers by a set of anti-return valves and pressurecontrol valves. Each low-pressure chamber 325 is connected to thehigh-pressure chamber 327 that is diametrically opposed to it by ananti-return valve 328 which opens in the direction from the chamber 325to the chamber 327, in parallel with a pressure control valve 329.

[0298] In this case, there is no intersection, as in the embodiment ofFIGS. 14 and 15, and as symbolized in FIG. 17, of the connectionsbetween the low-pressure and high-pressure chambers of two implantsmounted in parallel. Moreover, there is only one type of low-pressurechamber.

[0299] During an axial compression, the fluid contained and the conduits326 is, due to the thickness of the walls of the latter, expelled to thechambers 325 with a viscous fluid behavior. The walls of these are thanforced toward the outside, giving the implant its elastic behavior. Inthis respect, this implant behaves like the one in the precedingembodiment.

[0300] On the other hand, this implant has a particular behaviorrelative to non-axial loads. For example, in the this case of a loadexerted from the left side of FIG. 22, the low-pressure chamber 325 awill be compressed, while the chambers 325 b and 325 c will be at lowpressure. The wall of the chamber 325 a will then expand, while part ofthe fluid contained in this chamber will flow into the chambers 325 band 325 c through the conduits 326, further drawn by the prevailing lowpressure in these chambers.

[0301] When the movement is large enough and rapid enough, the outerwall of the low-pressure chamber 325 a comes into contact with theshell. The elastic behavior of the implant is then blocked, so that thepressure rises sharply in the low-pressure chamber 325 a. This pressurecan then become greater than the prevailing pressure in thehigh-pressure chambers 327 a which faces it, engaging the process forregulating the differential pressure described above in reference to thepreceding embodiment.

[0302] An implant according to this secure embodiment could therefore beused alone, while retaining the differential pressure regulationfunction.

[0303] Various implantations other than that represented and describedin reference to FIG. 13 can be envisaged for the implants justdescribed.

[0304]FIG. 23 shows a bone graft 330 disposed between two vertebrae 331.Two implants 305 such as those in FIGS. 14 and 15 have been placed inthe graft, symmetrically relative to the median plane of the patient'sbody. The interconnections between the implants and the functionalprinciples are the same as those described in references to FIGS. 14through 17.

[0305]FIG. 24 shows a single implant 332 as described in reference toFIGS. 18 through 22, implanted in a graft 333, which is itself disposedbetween two vertebrae 334. A solution of this type ensures goodperformance with regard to lateral as well as frontal flexions.

[0306] Articulated implants embodied according to the invention will nowbe described.

[0307]FIG. 25 shows an implant, or intervertebral prosthesis 400intended to be disposed, as shown in FIG. 26, between two vertebrae 401,in place of an intervertebral disk. This implant must therefore allowcertain movements between the vertebrae 401, contrary to what occurs inthe case of an arthrodesis.

[0308] The implant 400 generally formed by a shell comprising a bottom402 and a cover 403. The cover 403 rests on the bottom 402 as a resultof two spherical surfaces with the same radius, the surface 404 of thebottom which faces upward and the surface 405 of the cover which facesdownward. Thus, the cover 403 can pivot relative to the bottom 402around three axes.

[0309] The bottom 402 is hollow, so as to define a space 406 inside theimplant. The cover 403 forms a projection 407 into this spaces, the endof which projection is connected to the bottom by three innerviscoelastic “ligaments” 408, which will now be described in referenceto FIG. 27.

[0310] Each ligament 408 comprises a rigid hollow body 409 which issubstantially cylindrical and has, at one of its ends, an opening to theambient air 410. This opening is sealed by an ampulla, or elasticbellows 411. The bellows 411 is a cylinder closed at its end oppositethe opening 410 by a bottom 412, and its lateral wall forms a helicalfold 413 with a variable pitch which increases from the opening 410 tothe bottom 412.

[0311] The body 409 and the bellows 411 delimit a chamber 414 containinga hydraulic fluid which is supplied from, and whose pressure can beregulated by, a conduit 415 and a valve 416.

[0312] At the other end of body 40, the base 417 of this body supportsan annular cylindrical chamber 418 whose inner wall 419 and outer wall420 are also constituted by bellows. The chamber 418 contains ahydraulic fluid which is supplied from, and whose pressure is regulatedby, a conduit 421 and a valve 422.

[0313] At the center of the annular chamber 418, the wall of anothercylindrical chamber 423 is formed by a bellows 424. The chamber 423connects to the chamber 414 through a calibrated opening 425 cut intothe base 417 of the body 409. The chamber 423 is therefore supplied andpressurized from the chamber 414.

[0314] The end of the bellows 424 opposite the base 417 is sealed by aplate 426 which carries a support piece 427 passing through an opening428 of an end plate 429 of the annular chamber 418. The end plates 426and 429 are integral.

[0315] Formed inside the chamber 423 is a chamber 430 mounted on thebase 417 of the body 409 by means of posts 431. One of these posts 431is hollow a makes it possible to supply and to pressurize the chamber430 with hydraulic fluid from a conduit 432 and a valve 433.

[0316] The wall of the chamber 430, between the junction points of theposts 431 and the base 417, forms a bellows 434. The bottom of thechamber 430, which faces the base 417 of body 409, carries a needle 435which penetrates into the calibrated opening 425.

[0317] The implant is anchored at the projection 407 and at the bottom402 by its elements 409 and 427.

[0318] It is easily understood that the length of the ligament 409 is afunction of the pressure in the annular chamber 418, which determinesthe elongation of the bellows 419 and 420. This length can be adjustedby means of the valve 422.

[0319] Moreover, the coefficient of resistance of the ligament 409 is afunction of the free cross-section of the calibrated opening 425, andthus penetration depth of the needle 435. This coefficient can beadjusted by means of the valve 433.

[0320] Finally, with regard to its elasticity, the bellows is comparableto a helical spring with a variable pitch which becomes increasinglysteep as it is compressed and its spires progressively come intocontact. This bellows determines the elasticity of ligament 408 since,when the latter compressed, it elastically opposes the penetration ofthe hydraulic fluid into the chamber 414 through ti opening 425. Thecoefficient of elasticity can therefore be adjusted by means of thevalve 416 by pre-compressing the bellows 411 to a greater or lesserdegree.

[0321] It is noted that a structure similar to that of the ligament justdescribed could be used in place of the device of FIG. 7, in order torender its various functions adjustable.

[0322] An alveolar structure 500 made of elasticity which could replacethe three ligaments 408 of FIG. 25 will now be described in reference toFIGS. 28 through 31.

[0323] This structure is practically identical to that of the implant322 of FIGS. 18 through 21 (FIG. 28 has been schematized). It is noted,however, that in this case the structure 500 has an opening 501 oftriangular section for receiving a projection of the cover, similar tothe projection 407 and intended to form a pivot between the bottom andthe cover of the prosthesis.

[0324] The interconnections between chambers are the same as in the caseof the implant 322, and the functioning of the present prosthesis andthe implant are the same from the hydraulic standpoint.

[0325] The differences reside in the way in which the stresses areapplied. In this case, essentially transverse stresses are applied tothe low-pressure chamber 502 by the projection of the cover.

[0326]FIG. 32 shows one possible implantation of the prosthesis of FIGS.25 through 31.

[0327] This figure shows the bottom 503 and the cover 504 of theprosthesis. The bottom 503 is equipped with fittings 505 and the cover504 with fittings 506 for their respective attachment to a lowervertebra 507 and an upper vertebra not represented.

[0328] The various hydraulic chambers are connected by conduits 508 to aset of subcutaneous control buttons 509, particularly push-buttons,disposed behind the vertebrae. Safety devices are preferably provided inorder to prevent ill-timed operation of the buttons. In a variant, fullyhydraulic adjustment means could be provided, with a subcutaneous accesssite connected to the various chambers by a slide valve.

[0329]FIGS. 33 and 34 show, in partial perspective and cross-section,respectively, an anti-return valve which can be used in the invention.

[0330] These valve is composed of a conduit 510 connected to thehigh-pressure and a conduit 511 connected to the low pressure. Theseconduits are coaxial, and the end of the low-pressure conduit 511 isengaged inside the end of the high-pressure conduit 510. The end of theconduit 511 inside the conduit 510 is flat.

[0331] As long as the high pressure is greater than the low pressure,the end of the conduit 511 remains flat and the valve remains closed,thus preventing the possible of a flow from the conduit 511 to theconduit 510. But when the low pressure becomes higher than the highpressure, the end of conduit 511 opens and fluid flows from the conduit511 to the conduit 510.

[0332] Finally, FIGS. 35 through 39 illustrate a coxofemoral prosthesisembodied according to the principles of the invention.

[0333] This prosthesis is intended to be used after a fracture of theneck of the femur and a resection of its upper part. It comprises a pin600, one end of which is intended to be attached to the remaining partof the femur, and a hollow sphere 601 whose wall includes an opening 602to allow it to be penetrated by the end of the pin 600.

[0334] The upper end of the pin 600, inside the sphere 601, is integralwith a cylindrical head 603. The latter is capable of sliding andforming a piston in a circular opening 604 of an internal partition 605of the sphere. The axis of the head 603 and of the opening 604 passessubstantially through other end of the femur, at the level of the kneejoint.

[0335] The partition 605, along with the piston 603, delimits inside thesphere two chambers 606 and 607, which are respectively upper and lowerchambers. The chambers 606 and 607 contain viscoelastic devices whichdetermine the relative movement of the pin 600 and the sphere 601, as afunction of the stresses applied.

[0336] In one particularly simple embodiment, these viscoelastic devicescan be simply constituted by an elastic foam which fills the chambers606 and 607, and a calibrated opening formed in the head 603. The foamcontains a hydraulic fluid and an appropriate joint is disposed at thelevel of the opening 602.

[0337] However, the embodiment in FIGS. 38 and 39 is preferred.

[0338] In this case, the viscoelastic devices 608 are embodied in a formpractically identical to that of the structures 307 in the implants 305.The difference resides in the fact that the structures 307 are generallyof cylindrical shape, while the devices 608 have a shape which isgenerally hemispherical. But in a similar way, they are chiefly composedof a peripheral low-pressure chamber 609 and a center low-pressurechamber 610, separated by a wall 611.

[0339] Annular high-pressure chambers 612 formed within the thickness ofthe wall 611, are interposed with calibrated conduits 613 which connectthe low-pressure chambers 609 and 610. The intersecting interconnectionsbetween chambers are embodied as above.

[0340] When the prosthesis is stressed, the head 603 compresses one ofthe devices 608, while the other device is at low pressure. Everythingindicated relative to the functioning of the twin implants 305 remainsvalid in the present case.

[0341] It is noted that in this case, when a device 608 is compressed,its line of tangency with the inner surface of the sphere moves closerto the partition 605. The elastic outer wall surface then decreases,which has the effect of increasing the elastic rigidity of the device.

[0342] The interconnections between chambers are embodied as shown inFIG. 39, by borings 614 formed in the head 603 and in the pin 600. Theseborings emerge at the level of a control button box 615 (FIGS. 35 and36). This box is disposed subcutaneously so as to be easily accessible,in order to allow the necessary adjustment.

[0343] The implant 700 of FIG. 40 generally comprises a viscoelasticcell 701, for example like that in the implant 305 of FIG. 13 and thesubsequent figures, or like the ligament 408 of FIG, 27, as well as adistance adjusting element 702, in this case for adjusting the height,and a refill cell 703. These elements are mechanically disposed inseries, in support, with the half-pins 704, 704′ of the arthrodesis,which can belong to the two vertical members of a frame. The half-pins704, 704′ consequently support the pressure of the patient's body, whichis variable as a function of his posture.

[0344] The adjusting element 702 can be embodied as shown in FIGS. 41and 42, in the from of an expandable toric bellows, which can expandaxially. Its central free space allows it to house a protuberance of theviscoelastic cell.

[0345] In a variant, the adjusting element can be in the form of thedisk-shaped bellows 702′ of FIGS. 43 and 44.

[0346] The adjusting elements 702 (or 702′) can be connected by aconduit 705 to a tube valve 706 which can itself be connected to a pump707. Thus, it is possible to adjust the thickness of the element 702. Itis therefore possible to adjust not only the total length of theprosthesis, but also the angle formed between its upper part (thehair-pins 704) and its lower part (the half-pins 704′) by means of adifferential filing of two element 702 of the prosthesis.

[0347] It is noted that valve 706 itself can be implanted, in which caseit is accessed either by cutaneous incision or by means of an accesssite, or external, the conduit 705 being transcutaneous.

[0348] In another embodiment, represented in FIG, 46, the filling of theadjusting elements is carried out with the aid of a high pressurereservoir 708, in this case dilatable, and a slide valve 709. In asimilar way, the emptying of these elements occurs into a low-pressuredrainage collector 710, also dilatable, through another slide valve 711(or in the same way, through a three-way valve).

[0349] Moreover, a filling valve 712 makes it possible to fill thereservoir 708, and a drainage valve 713 makes it possible to emptyreservoir 710. The reservoirs 708 and 710 are implanted and the valves712 and 713 can be external or implanted, as in the case of the valve706. Generally, however, they will be implanted, since their accessshould be far less frequent than that of the valve 706.

[0350] The refill cells 703, whose function will be described below, areentirely similar to the adjusting elements 702. However, they areconnected to the high-pressure and low-pressure reservoirs 708 and 710not by slide valves, but by anti-return valves 714 and 715,respectively. The anti-return valves 714 are connected from the cells703 to the high-pressure reservoir 708, and the anti-return valves 715are connected from the low-pressure reservoir 710 to the cells 703.

[0351] The cells 703 serve as pumps for refilling the high-pressurereservoir 708. In effect, when the patient bends, for example to theright, the cell 703D is compressed. When the pressure in this cellsurpasses the pressure in the reservoir 708, the anti-return valve 714Dopens and fluid passes from the cell 703 to the reservoir 708.Simultaneously, the left cell 703G draws in fluid from the low-pressurereservoir 710.

[0352] A pressure control valve 716 prevents the high-pressure fromexceeding a predetermined value.

[0353] It is noted that if only angular corrections are desired, therefill device can be greatly simplified, and the refill cells inparticular can be eliminated. In effect, in this case it suffices toconnect the adjusting elements by means of a slide valve. When thepatient bends, for example to the right, the valve is opened so fluidpasses from right to left, then is closed again. When the patientstraightens, the height of the left side will be larger and that of theright side will be smaller.

[0354] The viscoelastic cells have not been described in thisembodiment. It is simply noted that in the case where they comprisehigh-pressure chamber, like for example the implants 305 or theligaments 408, these chambers can be connected to the high-pressurereservoir 708 by a valve, for example a slide valve. Thus it is possibleto easily rigidify the viscous behavior of these cells. The low-pressurechambers of the viscoelastic cells, for their part, can also beconnected to the low-pressure reservoir 710.

[0355]FIG. 48 shows a possible implantation for the elements justdescribed. The connecting conduits generally have the reference number717. It is noted that all these elements can have very small dimensions,and the hydraulic volumes can be very low.

[0356] The physical characteristic of the implants just described can bemodified postoperatively by any means, including entirely non-invasivemeans, whether in terms of their viscoelastic properties, theirdimensions, their lateral or antero-posterior inclination, or theiranti-rotational resistance.

[0357] By way of example, FIG. 49 illustrates an electronic controlcircuit for an implant of the type represented in FIG. 47.

[0358] This circuit is embodied in two parts, an extracorporeal part 720and an implanted part 721. Those two parts are in contact by means oftwo antennas 722 and 723, respectively.

[0359] The circuit part 720 comprises a power supply 724, a remotecontrol device 725, a detection and amplification module 726, and amonitor 727. The remote control device 725 controls a radio frequencymultiplexer 721 connected to the antenna 722.

[0360] The circuit part 721 also comprises a radio frequency multiplexer729 connected to the antenna 723. The multiplexer 729 is connected to aradio frequency/D.C. Voltage converter 730 which supplies electric powerto the other modules of the circuit part 721, namely a radio frequencyoscillator 731 and sensors 732, as well as actuators 733.

[0361] In the case of FIGS. 40 and 47, the sensors 732 can be, inparticular, pressure sensors in the distance control elements 702, andpossibly in the chambers of the viscoelastic cells 701. The actuatorscan comprise electrically operated valves such as the slide valves 709and 711. More particularly, the pressure sensors can comprise, for eachside of the patient, one sensor for each low-pressure chamber and onesensor for the high-pressure chamber. Pressure sensor can also beprovided on the means for attaching the implants, such as screws orhooks, as well as on the bone, possibly bridged.

[0362] When the doctor wishes to know and possibly to adjust thepressure in the elements 702, for example, he operates the remotecontrol device 725. The antenna 722, placed in proximity to the antenna723, emits a code that is detected and used by the implanted part 721.Moreover, the radio frequency is transformed into a D.C. supply voltagefor the sensors 732, the oscillator 731, and the multiplexer 729. Theimplanted part then in turn emits a code containing the pressureinformation, which is detected and displayed on the monitor 727. Theadjustment of the elements 702 by means of the electrically-controlledvalves 733 occurs whose in the same way.

[0363] It is noted that thanks to invention, it is possible to perform adetailed examination of the behavior of the implants. For example, inthe case of a vertebral implant, it is possible to measure its frequencyresponse, or its impulse response, by having the patient sit on a seatequipped with means for moving in any direction desired, and byrecording the response of the pressure sensors. The adjustment of thevarious stationary pressure levels can thus be determined with greatprecision.

[0364] It is noted that implant according to the invention can includeanalgesic neurostimulating means of a known type, as well as aprogrammable medication delivery pump.

[0365] Generally, for all of the implants described above which do nothave remote control by means of radio frequencies or the like, devicesare provided which are accessible either directly, as in the case ofsubcutaneous buttons, or by means of a benign intervention. The meansfor adjusting by remote control without physical contact can be rotaryvalves of the “sluice” type which are multidirectional, whose rotationis induced by an external rotating magnetic field. A spiral springre-establishes equilibrium in the closed position. It is advantageous tobe able to carry out the desired adjustments relatively often, either ina planned way, for example in order to progressively reduce thecoefficient of resistance as a graft consolidates, or as necessary, forexample in order to relieve pain.

[0366] Likewise, all of the above-mentioned implants can be providedwith improvements which have only been described in reference to certainembodiments. This is the case, for example, with the dimensionaladaptation provided in the implants of FIGS. 14 and 27. A disposition ofthis type is particularly useful in any implant intended for a child whois still growing, or an elderly person whose size is gradually dressing.

[0367]FIG. 51 shows two individual implants, a right-hand one and aleft-hand one, generally designated by 1′ and comprising a lower end rod2′ and an upper end rod 3′ between which there is interposed adeformable hydraulic element 4′ which has been shown in the form of acylinder/piston assembly, but which in reality would instead be in theform of a metal bellows so as to prevent the escape of hydraulic liquid.Alternatively, this deformable element can be of the telescopic type orof an otherwise deformable type, for example a cylindrical cell which iselastic longitudinally but not transversely. The rods 2′ and 3′ areguided in the continuation of one another so as to move along the samevertical axis and to take up distanced or close positions as a functionof the extent of filling of the deformable element 4′. The lower andupper ends 2′, 3′ have attachment means 5′, 6′ in the form ofarticulations. Extending parallel to the element 1′ there is a rigidjoining rod 7′ which terminates in lower 8′ and upper 9′ attachmentmeans in the form of articulations. The rod 7′ extends essentiallyparallel to the individual element 1′, but it could be more inclined,and can be made integral with this element, although this is not arequirement. Connected to each element 1′ there is a lower pedicle screw10′ and an upper pedicle screw 11′ whose threaded parts are fixed in thecorresponding vertebral pedicles. The posterior end of the pediclescrews 10′, 11′ is received in the ends 5′ and 6′ in the manner of anarticulation permitting an angular clearance at least in the planeconstituted by the element 1′ and the joining element 7′. Ifappropriate, the articulation can have a supplementary degree of freedomor can be of spherical shape giving a degree of freedom in rotation inall directions.

[0368] In an intermediate position, the screws 10′, 11′ are fixed andarticulated respectively on the ends 8′ and 9′ of the joining element 7′by articulations also permitting an angular clearance in the commonplane, for example the sagittal plane, of the element 1′ and of itsjoining element 7′.

[0369] The two deformable elements 4′ of the pair of individual implantswhich form the complex implant shown in the drawing are connected via aline 12′ on which there is arranged a hydraulic circuit element 13′,shown in the example in the form of a slide valve.

[0370] The configuration shown in FIG. 51 permits antisymmetricalrotation movements of the pedicle screws.

[0371] It is assumed that the pedicle screws have been screwed in theangular positions shown on the drawing, that the hydraulic circuits andthe elements 4′ are entirely filled with hydraulic liquid and that thevalve 13′ is in the closed position. In such a situation, the pediclescrews are blocked in their angular position shown on the drawing. Inthis position, the internal volume of the left-hand element 4′ issmaller than that of the right-hand element 4′, which corresponds to amore closed angle. If the valve is now opened, it will be appreciatedthat the pedicle screws are going to be able to pivot about the centreof articulation of the points 8′ and 9′ at the end of the joining rod,as a function of the increase or reduction in the length of thecorresponding element 1′, itself dictated by the volume of liquidpresent in the associated deformable element 4′. Given the communication12′ between the two deformable elements 4′, it will also be appreciatedthat any variation in the volume of liquid of one of the elements iscompensated by an inverse variation in the volume of the other in such away that the rotation of the pedicle screws in one direction on one ofthe elements is translated into a rotation of the pedicle screws in theother direction and having essentially the sane absolute angular value.

[0372] This property can be made use of in various applicationsdescribed in the abovementioned EP and US applications.

[0373] If the hydraulic circuit element 13′ is a viscoelastic regulatingelement which considerably brakes the passage of liquid, or prohibitsthis in the event of an abrupt angular movement of the pedicle screws,the vertebrae can be left free to pivot relative to one another in thefrontal plane of the spine when the movements are slow, and, bycontrast, the screws can be immobilized or their rotation considerablybraked when the movements have a tendency to be rapid. In this way it ispossible to obtain a damping effect in rotation while at the same timepermitting a freedom of rotation for slow movements.

[0374] If the element 13′ is an element with which it is possible toimpose the supply of the hydraulic liquid into one of the deformableelements 4′ and the withdrawal of the same volume of liquid from theother element 4′, this supply then being followed by a closure of thecommunication, it is possible, some time after having implanted the twoindividual implants with given angles of pedicle screws, to initiate anexternal command, for example a transcutaneous magnetic command, inorder to modify the angle and thereby to effect in small stages acorrection of a vertebral deformation.

[0375] Means can be provided for exerting a continuous or intermittentconstant pressure in the bellows 4′ in such a way as to permanentlystress the skeletal parts whose position is to be corrected.

[0376] Of course, by using different hydraulic circuits, it is possibleto achieve the two functions which have been described, as has beenexplained in the above mentioned applications.

[0377] Of course, according to the invention, it is also possible to useeach individual implant with its joining rod as a totally independentelement and to control each of the elements separately without anyinterconnection 12′, in order to ensure some or all of the functions ofmodification of length and thus of angulation, as well as viscoelasticdamping.

[0378] In a preferred manner, the implant element is also combined witha device with which it is possible to supply a deformable element 4′with high-pressure liquid, if this is necessary, from a deformablebellows functioning, for example, as a pump actuated by the body, as hasbeen described by the abovementioned application. In the case of the useof two individual implants for forming a complex implant, case theshown, this supply and discharge means can be common to both implants.

[0379]FIG. 52 shows a complex implant similar to that in Claim 1, but inwhich the joining rods 7′ are articulated at the free ends or heads ofthe pedicle screws while the deformable individual element isarticulated in the intermediate position, this giving an inversion ofthe movement of rotation relative to that shown in FIG. 51, andadditionally moves the centre of rotation of each pedicle screwrearwards.

[0380]FIG. 53 shows a complex implant which is identical, for theindividual implants 1′, to that shown in FIG. 2. By contrast, thejoining element 7′, which was a signal rigid rod, has been replaced by ajoining element 14′ formed in the manner of an individual implant andthus comprising two ends 15′, 16′ which are capable of movinglongitudinally relative to one another with interposition of adeformable hydraulic element 17′, by which means it is possible to havea joining element whose length can be modified if necessary or which canitself have a damping affect analogous to that of the actual implant 1if this function is present.

[0381] Preferably, the two elements 17′ of the two individual implantsshown are connected via a channel 18′ with interposition of a hydrauliccircuit element 19′.

[0382] The desired functions will then be determined by the nature andcontrol of the hydraulic regulating elements 13′ and 19′ and it will beappreciated that in such a design it is possible, if so desired, to makethe implant element 1′ and its joining clement 14′ interchangeable andthus to fix the centre of rotation of the pedicle screw either at theend 5′ (or 6′) or at the end 8′ (or 9′) or even at another point betweenthese articulations.

[0383]FIG. 54 is a diagrammatic representation of a practical embodimentof the device in FIG. 53 (on which the lines and the hydraulic circuitelements 13′, 17′ are not shown). The individual implant shown includesa hydraulic bellows 4′ bearing on its upper face a component with an armforming the rod 3′, on its lower face a plate with an arm for formingthe lower rod, the said rods having articulations 5′ and 6′ for thepedicle screws 10′, 11′. The element 14′ includes a hydraulic bellows17′ whose lower plate bears an arm 15′ and the upper end an arm 16′, thesaid arms bearing, at their free end, the articulations 8′, 9′ receivingthe posterior ends of the screws 10′, 11′. If appropriate, one arm ofthe element 1′ and another arm of the element 14′ can be mechanicallysecured or, by contrast, all these elements can be left independent, thelink then being made only by the screws 10′, 11′.

[0384] Thus, it is possible to arrange the bellows spatially one belowthe other and to form an implant according to the invention with agreatly reduced size.

[0385] In FIG. 55, now, a device has been shown which is analogous tothat in FIG. 1, the only difference being that one of the deformabledevices or bellows 4′ has been replaced by a deformable device 20′,which, furthermore can also be made in the form of a bellows and inwhich the points of attachment of the lower 2′ and upper 3′ arms havebeen inverted, in such a way that an increase in the volume of thedevice 20′ entails, in contrast to the increase in volume of the device4′, a shortening of the implant element instead of a lengthening.

[0386] It is thus possible, by virtue of the interconnection via theline 12′ and the element 13′, to obtain symmetrical rotation movementsinstead of antisymmetrical rotation movements. In other words, therotations of the screws 10′, 11′ on the right-hand side of the spine areidentical to the rotations of the screws of the left-hand element, andof the same direction.

[0387] It is thus possible to obtain movements of flexion or extensionof the spine this time in the sagittal plane.

[0388] As in the other cases, this can be made use of either to provokea lordosis effect or vice versa, depending on the desired aim, forexample by acting in stages from an external command, or to achieve aperfectly symmetrical damping effect in the case of spontaneous movementof rotation between the vertebrae, or else to achieve the two functionssimultaneously by virtue of more complex circuits.

[0389]FIG. 56 shows a configuration according to FIG. 55, but in whichthe joining elements 7′ are arranged, as in FIG. 2, in such a way thatthe centre of rotation of the pedicle screws is arranged at the ends ofthe screws.

[0390] Alternatively, it is also possible to combine the solution ofFIG. 51 and of FIG. 52, placing the element according to FIG. 1 on theright of the sphere, for example, and an individual element according toFIG. 2, on the left, it being understood that in this case the angularvariations of the right-hand screws will at all times be the inverse ofthose of the left-hand screws, but of more different absolute value.

[0391]FIG. 57 shows a complex implant which also permits symmetricalrelations in the sagittal plane, as indicated in FIG. 56, but in whichthe joining rod 7′ of each of the individual implants has been replacedby joining elements which are themselves of variable length, the one onthe left being a joining element 14′ as shown in FIG. 53, while thejoining element on the right also has an inversion of action in the areaof the bellows. In other words, an arrangement is obtained in which themovements of rotation on left and right are symmetrical in the sagittalplane.

[0392]FIG. 58 is a diagrammatic representation of an embodimentanalogous to FIG. 54, but in which it will be seen that, by invertingthe bellow ends on which the arms are fixed, a movement is obtained inthe opposite direction to that in FIG. 54.

[0393] Referring to FIG. 59, this shows an assembly of two individualimplants, of which the left-hand implant 20′ includes two end pieces21′, 22′ which are able to move in the continuation of one another, withinterposition of a deformable element 23′ analogous to the deformableelement 4′. The ends 24′ and 25′ of the pieces 21′, 22′ have fixationholes enabling anchoring means, for example pedicle screws to besecured. In contrast to the representations in the preceding figures,these fixation means at the ends 24′, 25′ do not necessary permit apivoting of the pedicle screws, such as the screws 10′ and 11′, and bycontrast they can be formed by bores or eyelets which permit rigidconnection without any possibility of pivoting of the screw relative toits corresponding end 24′ or 25′.

[0394] The right-hand implant 26′ also has two end pieces arranged inthe continuation of one another, namely 27′ and 28′, of which the ends29′ and 30′ are analogous to the ends 24′ and 25′ so as to receive thepedicle screws without any possibility of movement of the screw relativeto the end which bears it. The end piece 27′ has, starting from the end29′, a part in the form of an elongate threaded rod which terminates inthe movable part of a deformable hydraulic element 32′ analogous to theelement 23′ or to the element 4′. It will thus be appreciated that ifthe deformable element 32′ deforms and provokes a relative movement, forexample of spacing apart or distraction, between the pieces 27′ and 28′,the movement of the piece 27′ relative to the piece 28′ will provoke therotation of the piece 27′ on account of the fact that its threaded rodmoves in the fixed nut 31′. The result of this is that the end 29′ isdriven relative to the end 30′ in a displacement movement simultaneouslyof translation and rotation. Consequently, the end of the pedicle screw(not shown) borne by the piece 29′ of the movable piece 27′ willdescribe a helical movement whose axis is formed by the alignment of thepieces 27′ and 28′.

[0395] If the two elements 20′ and 26′ are connected as is shown in thefigure, by a valve 13′ in a line 12′, it will be appreciated that, as inFIG. 51, the reduction in the volume of the movable element 23′ willtranslate into an increase in the volume of the movable element 32′ and,thus, of the opposed axial displacements of the implants 20′ and 26′,with, in addition, the movement of rotation of the piece 27′.

[0396] Reference is now made to FIG. 60. In this figure, the element 20′is identical to that in FIG. 59. Like the implant 26′, the other implant33′ has an end piece 28′ terminating in an end 30′ which permits thefixation and blocking of an anchoring screw. By contrast, the element33′ includes a second end piece 34′ with its end 35′ for receiving andblocking the anchoring screws, this piece 34′ being connected to theelement 28′ in such a way as to be immobilized in translation but freein rotation about the axis of t piece 34′. The movable part 36′ of thedeformable element 39′ has a piece in the form of a tapped nut 37′through which a threaded part 38′ of the piece 34′ passes. It will thusbe appreciated that when the deformable element 39′ deforms, themovement of the movable piece 36′ will provoke a rotation of the endpiece 34′ about its axis, but without translation relative to the endpiece 28′, in such a way that the end 35′ turns without displacement intranslation relative to the end 30′.

[0397] In the embodiment shown in FIG. 60, by virtue of the valve 13′, avariation in the volume of the deformable element 20′ will translateinto an inverse variation in the volume of the deformable element 39′,in such a way that the lengthening of the element 20′ translates into arotation of the end 35′ in one direction, whilst the shortening of theelement 20′ produces a rotation of the end 35′ in the oppositedirection.

[0398] Of course, all the other control combinations can be realized,for example in the case of FIG. 59, in order to provoke identicallengthening of the elements 20′ and 26′ while ensuring the rotation ofthe piece 27′.

[0399] Referring to FIGS. 61 and 62, embodiments of the implant 26′ inFIG. 59 are shown. It will be seen that the end pieces 25′ and 29′ havea streamlined shape in the form of a dolphin's snout and have transversepassages forming the ends 29′ and 30′ and permitting the fixation of apedicle screw in an entirely traditional manner. In this figure, theportion forming the nut 31′ is borne by the lower piece 27′. This nut31′ is traversed by a threaded rod 40′ which is rigidly supported by theupper end piece 28′ in such a way that the axial displacement of thisrod provokes the rotation of the piece 28′ relative to the piece 27′.The threaded rod 40′, as will be seen in FIG. 62, passes into a pot 41′which is received in a leaktight manner inside the hydraulic bellows 32′acting as movable element, and the rod 40′ can turn in this pot aboutits axis while being retained inside the pot by a securing ring 42′. Itwill be seen from this that it is also possible to give the overallimplant an elongate streamline shape particularly appropriate for goodcohabitation with the surrounding tissue.

[0400] Referring to FIG. 63, this shows an embodiment of an implant 33′according to FIG. 60 with an upper end 28′ and a lower end piece 34′which has arms 43′ ending in a bearing 44′ inside which there can freelyturn, while being retained axially by a securing ring 45′, a threadedrod 46′ which is integral with the piece 28′ and is capable of turninginside a nut 47′ of a pot 48′ fixed in a leaktight manner on the metalbellows 49′ at the end integral with the end piece 34′. It will beappreciated that any movement of the bellows provokes an axial movementof the nut 47′, which provokes a rotation without axial movement of thepiece 28′ relative to the piece 34′.

[0401] We now describe the use of a double implant for the correction ofscoliosis in a patient having an angle of scoliosis a1 between the twoscoliotic vertebral stages. During the operation, the surgeon employstraditional means to establish a preliminary correction bringing theangle of scoliosis to the value a2<a1. He then places the two individualimplants on either side of the vertebral column between the twovertebral stages in question, with the valve 13′ open, which permits theshortening of one of the individual implants and the compensateelongation of the other individual implant, and he fixes the twoelements with the aid of their pedicle screws. It then suffices tore-close the valve 13′ so that the two individual implants are blockedin their position without any possibility of movement and they maintainthe scoliotic part of the vertebral column in the angle a2. From thismoment onwards, all the loads are borne by the prosthesis constituted bythe double implant.

[0402] After a reasonable postoperative period during which the stressesare supported essentially by the prosthesis, the neutral point of thevertebral column will adapt by virtue of the reorganization of theskeletal and paravertebral tissues, and this will reduce the load on theprosthesis in the standing position. It is possible either to estimatethis reduction in load or to provide the prosthesis with pressuresensors which can be interrogated, preferably noninvasively, as isalready well known, and which will indicate that the vertebral columnhas reached a state of equilibrium.

[0403] A new adjustment will then be made by asking the patient to bendsideways to reduce the value of the angle a of scoliosis to a valuea2<a1 after opening the valve 13′, which renders the two implantsmovable. Once this angle a2 has been obtained, the valve is closed againso that the two implants maintain this new position and prevent thereturn to a greater angle of scoliosis. This blocking of the prosthesiscauses the patient the sensation of an obstacle which will graduallydisappear until such time as a new equilibrium is found.

[0404] By means of a succession of these maneuverers, it is thuspossible to reduce or even eliminate the angle of scoliosis and toremove the prosthesis.

[0405] It will be appreciated that the same principles can be used forgradually re-establishing kyphosis or lordosis by used pairs of implantswhich are arranged, for example, in accordance with the figures.

[0406] Likewise, by a pair of prostheses as in FIG. 9, for example, itwould be possible to gradually reduce kyphoscoliosis.

[0407]FIG. 64 shows a transverse cross section of an implant in arefined embodiment of the invention.

[0408] This implant 1′ includes two end pieces 51′ and 52′ in the shapeof a dolphin's head, having at their outermost parts holes or eyelets53′ and 54′ through which it is possible to engage pedicle screws whoseheads can be fixed rigidly in the area of the holes 53′, 54′.Alternatively, these holes can be arranged in such a way as to permit anarticulation of the head of the pedicle screw and thus an angulardisplacement between the end element and the screw which it bears.

[0409] Arranged between the two end pieces 51′ and 52′ there is a thirdpiece 55′ which is movable relative to the two ends. The piece 55′ has astirrup shape, of which one of the branches 56′ supports a metal bellows57′ in a leaktight manner, the free end of which bellows is fixed in aleaktight against a piece 58′ which is able to slide relative to thestirrup 55′ and chambers, in the manner of a journal, by virtue of asecuring ring, but axially nonmovable relative to the piece 58′, athreaded rod 59′ which passes through a complementary tapped hole of thesecond branch 60′ of the piece 55′. It will thus be appreciated thatwhen the deformable element constituted by the bellows 57′ deforms. Thethus provoked axial displacement of the rod 59′ integral with the upperend 3′ entrains the rotation of this rod in the fixed nut formed in thebranch 60′, and consequently a simultaneous movement of translation androtation of the end piece 52′ relative to the piece 60′.

[0410] Arranged inside the end piece 51′ there is a leaktight cavity 61′which serves as a high-pressure chamber and in which there is a bellows62′ which is hermetically sealed and in which a vacuum has beenestablished, the stiffness of this bellows, however, being sufficient toensure that it tends spontaneously to deploy and increase in volume evenwhen it is surrounded by the high pressure prevailing in the chamber61′. The chamber 61′ communicates via a nondeformable conduit 63′ withthe inside of the metal bellows 57′ by way of a high-pressure valve 64′lodged in the branch 56′, this valve having a tubular slide of soft iron65′ which is normal held back by a spring in the position closing offthe passage towards the bellows 57′. It will be appreciated that whenthe plunger core 65′ is brought into a position of opening counter tothe valve spring, liquid at high pressure in the chamber 61′ will runalong the conduit 63′ and enter the bellows 57′, the high pressure inthe chamber 61′ being maintained by the concomitant deformation of thesealed bellows 62′. This inflow of liquid provokes the displacement ofthe piece 58′ towards the branch 60′ and, consequently, the distractionand rotation of the end piece 52′ relative to the central piece 55′.

[0411] The inside of the bellows 57′ also communicates, by way of alow-pressure valve 66′ equipped with a plunger core identical to thecore 65′ situated in the piece 58′, with the volume 67′ surrounding thevarious pieces contained inside the deformable impermeable sleeve 68′,at the two ends of which the ends of the pieces 15′ and 52′ emerge, thisvolume 67′ forming the low-pressure volume. It will be appreciated thatwhen the valve 66 is opened, liquid contained in the bellows 57′ willexit and spread through the low-pressure volume 67′, thus permitting aretraction or compression of the bellows 57′ and a simultaneous rotationof the piece 52′ in the opposite direction.

[0412] The high-pressure reservoir 61 is recharged by way of a metalbellows 69′ which is of a diameter substantially smaller than that ofthe bellows 57′ and which is interposed between the pieces 51′ and 55′.When the pieces 51′ and 55′ move away from each other, this bellows 69′expands and aspires liquid from the low-pressure chamber 67′ by way of anonreturn valve 70′. By contrast, when the pieces 51′ and 56′ closetogether, the high pressure generated in the bellows 69′ causes liquidat very high pressure to enter the high-pressure chamber 61′ by way of anonreturn valve 71′.

[0413] It is not necessary for the deformation of the bellows 69′ to beof a great amplitude; on the contrary, it is preferable for the gapbetween the piece 51′ and the piece 56′ to be small and for the courseof oscillation between the pieces 51′ and 55′ to be limited, amultiplicity of oscillations, for example, as the subject walks orchanges position of his/her body sufficing to generate the high pressurepermitting supply to the chamber 61′.

[0414] In such an embodiment, as long as neither of the valves 64′ and66′ is open, the two pieces 51′ and 52′ can move relative to one anotheronly by a very short distance, and this thus ensures that the twoskeletal elements to which they are anchored, for example two vertebrae,are maintained in the chosen position. The device for establishing highpressure can even be used to obtain a certain viscous damping of thesmall displacements permitted between the pieces 51′ and 55′.

[0415] It will also be appreciated that having arranged thehigh-pressure and low-pressure valves 64′, 66′ on either side of thebellows 67′, one or other of these valves can easily be actuated,according to choice, for example by means of a strong magnet placed onthe skin in line with one of the valves in order to attract theferromagnetic plunger such as 65′ towards the left of the drawing and toopen the valve.

[0416] It will of course be appreciated that it would be possible toform an implant analogous to that which has just been described, butarranged so as not to provoke rotation between the two end pieces, butsimply a movement of distraction or compression. It would also bepossible to form an implant such as that in FIG. 13 using most of thestructural arrangements in FIG. 14 so as to form an implant uniquelywith rotation.

[0417] By combining with an implant of this type a joining rod analogousto the rods 7′, and by forming at the ends of the pieces 51′ and 52′articulation bearings permitting a pivoting of the pedicle screwsrelative to the said ends, it is also possible to form implantsaccording to FIGS. 51, 52, or 55, or 56.

[0418] In the case where use is made of a large number of implantsaccording to the invention, arranged along the vertebral column betweendifferent levels of the spine, it is also possible to provide a singlehigh-pressure reservoir and a single low-pressure reservoir as well as asingle deformable element for establishing high pressure, this reservoirassembly being arranged away from the various individual implants andbeing connected to each of these by a low-pressure conduit and ahigh-pressure conduit, the implants themselves in this case not havingany hydraulic deformable element other than the motor bellows acting asbellows 57′.

[0419] Also, the controllable valves, such as the valves 13′, 19′ or 64′or 66′, instead of being controlled directly by way of a ferromagneticplunger capable of being attracted by a magnet placed on the surface ofthe skin near the valve, could be controlled, in a hydraulic mannerknown per se, by a small pilot valve which is easier to actuate becauseit has a plunger of lower inertia, the pilot valve addressing a controlpressure to the actual switching valve in order to open the latter, andthe closure of the pilot valve, by contrast, provoking the closure ofthe main valve.

[0420] It will also be appreciated that it is possible to limit themovement of one of the ends relative to the other by providingtraditional abutment means between the two pieces, which come into forceif the travel of the deformable member or of the motor bellows exceeds adesired amplitude. Thus, this provides an element of safety in the caseof a fault in the functioning of the implant which prevents it fromexactly maintaining the desired position, for example escape of liquidor conduit deformation or excessive deformation of a bellows.

[0421] The implants according to the invention are preferably deliveredwith a temporary removable element which holds them in a position ofdesired spacing between the two end elements and which the surgeonremoves once he has fitted the implant and fixed the pedicle screws orother anchoring means at the ends of the implant.

[0422] The invention also relates to a therapeutic surgical procedurefor modifying the position of two portions or elements of the skeleton,for example two vertebrae, in which procedure at least one implantelement according to the invention is fitted, one of the ends is fixedby an anchoring means to one of the portions or elements of theskeleton, and the other end is fixed by an anchoring means to the otherportion or element of the skeleton, if appropriate after having carriedout a preliminary correction of the relative position of the said twoportions or elements, the approach route and the tissues operated on areleft to heal, then, preferably by non invasive control means, acorrective displacement or force is produced causing correspondingstressing of the two end pieces of the implant, or the anchoring means,relative to one another.

[0423] This displacement can be provoked directly by the patient's bodyand, in this ease, the displacement is permitted by permittingdeformation of the movable element, for example a hydraulic bellows,then, when the displacement has been completed, all subsequentdisplacements are prohibited by blocking the said deformable element.

[0424] In another embodiment, in order to provoke the displacement, adeformation of the movable element is temporarily provoked by applying aforce with which it is possible to obtain the desired displacement,after which the movement of the deformable element is once again blockedand prevented.

[0425] In a third embodiment, by contrast, the movable element isallowed to exert a permanent force, preferably constant or possiblyprogressively variable, between the two ends and thus the two portionsor elements of the skeleton, with an intensity of force which isinsufficient to provoke an abrupt modification of dimension and anattack on the tissue opposing this dimensional variation, but which issufficient to provoke, as is known per se in the field of surgery, aslow deformation and an adaptation of the various tissues until thedesired corrected position is reached.

[0426] Such a procedure is particularly suitable for correction ofscoliosis or kyphoscoliosis.

[0427] When a force is exerted between two skeletal elements by means ofan implant according to the invention, this force can advantageously befrom a few daN to 25 or 30 daN.

[0428] The device can advantageously include force or pressure sensorsfor limiting or regulating the force to be exerted. Such miniaturizedsensors are available on the market.

[0429] It has been seen that the non invasive control means can bemagnets which, from outside the body, can displace or attract aferromagnetic mass, such as a valve slide, counter to a spring or anelastic return means which brings the mass back to its initial positiononce the magnet bas been removed.

[0430] It is also possible to use an external device which creates amagnetic or electromagnetic rotary field which, inside the body, turns arotary piece, for example a rotary slide of a valve.

[0431] This application is based upon the French Patent Applications No.96 09157, filed Jul. 22, 1996, and No. 98 05549, filed on Apr. 30, 1998,the disclosures of which are hereby incorporated by reference thereto intheir entireties and the priorities are hereby claimed under 35 USC 119.

What is claimed is:
 1. A skeletal implant of the type to be used forconnecting at least two elements (4, 5) of the skeleton, said implantcomprising at least two parts (7, 8), each of which is capable to beconnected to one of said elements, said at least two parts being movablewith respect to each other, wherein there is provided a damping device(9) having an adjustable damping coefficient between said at least twoparts, said damping device being responsive to non invasive controlmeans to adjust said adjustable damping coefficient.
 2. A skeletalimplant of the type to be used for connecting at least two elements (4,5) of the skeleton, said implant comprising at least two parts (7, 8),each of which is capable to be connected to one of said elements, saidat least two parts being movable with respect to each other, whereinthere is provided a force exerting device, between said at least twoparts, to exert a force between said at least two elements of theskeleton, said force exerting device being responsive to non invasivecontrol mean, to establish and to cancel said force.
 3. A skeletalimplant of the type to be used for connecting at least two elements (4,5) of the skeleton, said implant comprising at least two parts (7, 8),each of which is capable to be connected to one of said elements, saidat least two parts being movable with respect to each other, whereinthere is provided a means authorizing a travel between said at least toparts, from an initial starting position to a displaced position, saidmeans authorizing a displacement being responsive to non invasivecontrol means to authorise and interrupt this displacement and to adjustsaid displaced position.
 4. A skeletal implant as claimed in claim 2,wherein the intensity of said force is adjustable through said controlmeans.
 5. A skeletal implant as claimed in claim 2, wherein said forcecan be canceled or adjusted at an adjustable position of one of saidparts with respect to the other part.
 6. A skeletal implant as claimedin claim 3 wherein said means authorizing a displacement are, at leastpartially, reversible to authorise a displacement in a directionopposite or different to a direction of a precedent displacement.
 7. Askeletal implant as claimed in claim 3 wherein said means authorising adisplacement are also responsive to a force or pressure sensor on saidimplant, and.
 8. A skeletal implant as claimed in claim 2 comprising atleast a force, pressure or distance sensor on said implant and/or onbone element.
 9. A skeletal implant as claimed in claim 3 comprising atleast a force, pressure or distance sensor on said implant and/or on abone element.